bluuebunny/crossref_metadata_2025 huggingface dataset:
Synsedimentary submarine slope failure and tectonic deformation in deep-water carbonates, Cow Head Group, western Newfoundland
Authors: Coniglio Mario
Published: April 2011

The Cow Head Group, interpreted as a southeast-dipping base-of-slope carbonate apron, contains intraformational truncation surfaces and slide masses. Synsedimentary shear zones are formed (1) below intraformational truncation surfaces; (2) in the basal parts of slide masses; and (3) in the shallow subsurface because of downslope creep. Shear zones are characterized by a variety of synsedimentary deformation structures. Limestones are subject to folding, brecciation, rotation of fragmented beds, and the development of fitted-lenticular bedding. In the interbedded shales, there is both disruption of fine laminations and small-scale isoclinal folding and faulting. Outcrops characterized by these features and the lack of truncation surfaces or slide masses may reflect minor downslope creep. The presence of truncation surfaces, slide masses, and shear zones indicates deposition on an unstable sloping surface.The recognition of intraformational truncation surfaces and slide masses usually requires extensive strike exposure, which when lacking, (e.g., drill cores), limits the potential of these large-scale features as useful indicators of slope deposition. In the Cow Head Group, the recognition and proper interpretation of the common, small-scale deformation structures of synsedimentary shear zones provides evidence for slope deposition that is independent of other sedimentologic, stratigraphic, and regional data.In some parts of the Cow Head Group, "wrinkled" limestones characterized by a prominent dome-and-basin morphology reflect layer-parallel shortening related to tectonic deformation. The deformation of these limestones was previously considered to be synsedimentary, but their association with late-diagenetic precipitates and tectonic stylolites, in conjunction with their continuity and regularity, distinguishes these folds from those produced during synsedimentary deformation.
In situ measurements of moisture and salt movement in freezing soils
Authors: Gray D. M. , Granger R. J.
Published: April 2011

The paper presents the results of field studies on the movement of moisture and salts during freezing of Prairie soils. It is shown that large fluxes of water can migrate to the freezing front and move upward into the frozen soil above. The fluxes are largest in light-textured soils (e.g., silt loam) having a water table at shallow depth. However, substantial amounts of soil moisture may also move in silty clay, silty clay loam, and clay soils under dryland farming provided there is sufficient water present to support capillary flow.The dynamics of soil moisture transfer under natural conditions as a result of freezing involves movement of water in both vapor and liquid phases. In the shallow surface layer of soil, to a depth of 300–400 mm, vapor flow predominates; in the depth below, water usually moves primarily as a liquid. It is demonstrated that the accumulation of ice with time increases because of the downward movement of the freezing front and the upward movement of water into the frozen soil above. In a silt loam with large fluxes, the ice content of the frozen zone rapidly reaches a level (80–85% pore saturation) where measurable migration ceases. Conversely, in a silty clay the movement of moisture into the frozen soil is observed to continue throughout most of the freezing period, and the ice content reaches 93% pore saturation. The greater movement in the finer grained soil is attributed to a higher freezing-point depression, a larger number of capillary pores, and a higher concentration of soluble salts in the liquid films.A close association is observed between changes in the ice content and electrical conductivity of a silt loam after freezing. In a silty clay the agreement is less clear, probably the result of the exchange of ions between the migrating liquid water and the clay particles. Maximum amounts of exchangeable ions moving into a 1 m depth of soil by the freezing action are estimated to be 11.9 t/ha in a silt loam and 15.7 t/ha in a silty clay loam.Data showing the redistribution of water and salts during thawing are also presented and discussed.
Geochemical trends in the Ackley Granite, southeast Newfoundland: their relevance to magmatic–metallogenic processes in high-silica granitoid systems
Authors: Tuach J. , Davenport P. H. , Dickson W. L. , Strong D. F.
Published: April 2011

The Ackley Granite, occupying an area of approximately 2700 km2, was intruded at about 355 Ma across the boundary between the Avalon and Gander tectonic terranes of southeast Newfoundland. It is dominated by K-feldspar-megacristic and equigranular biotite-bearing granite with subordinate granodiorite, but 10 separate phases have been recognized, also including hornblende- and muscovite-bearing varieties. Small aplite–pegmatite type molybdenite deposits occur in a southwest lobe, and cassiterite–wolframite-bearing quartz–topaz greisens are found as steeply dipping veins and pods within a south-central lobe of the pluton. A geochemical study of 357 rock samples, randomly distributed on a grid of 2 km spacing, shows systematic geographic variation in the concentrations of a range of elements.The concentrations of silica and some other elements show a relatively abrupt change approximately 10–15 km west of the projected boundary between the Avalon and Gander terranes, indicating that the different terranes had some influence on magma compositions, presumably as source rocks, that was preserved through subsequent ascent, cooling, and crystallization. Other elements change along smoother trends and support a model for the southeastern part of the Ackley Granite magma chamber (2100 km2) analogous to those inferred for chemically layered, high-silica ash-flow tuffs. This model entails a process of convective fractionation and (or) liquid-state diffusion that was responsible for early enrichment and depletion of certain elements in the magma and was accompanied by volatile exsolution and mineralization, especially in magma with more than 74% SiO2.Overall, the southeastern Ackley Granite has "I-type" granite affinities, evolving to "A-type" affinities in the shallower, more silicic mineralized varieties. This study indicates that neither the current concepts for generation of different types of granite nor the metallogenic concepts linking Mo and Sn–W deposits to specific types of granite are generally applicable. We suggest that high-level magmatic processes are adequate to produce such features and that any high-silica granitoid pluton that exhibits extreme enrichment of the large-ion lithophile elements and depletion of Ba and Sr is a potential host to granophile deposits.
Stratigraphic, isotopic, and mineralogical evidence for an early Holocene thaw unconformity at Mayo, Yukon Territory
Authors: Burn C. R. , Michel F. A. , Smith M. W.
Published: April 2011

Ice-rich glaciolacustrine sediments near Mayo, Yukon Territory, reveal a thaw unconformity in the form of truncated ice wedges and abrupt changes in cryotexture. The unconformity has been radiocarbon dated at 8870 ± 200 years BP, which is within the Holocene period of optimal climatic conditions in northern Yukon and the Mackenzie Delta area reported by other workers. Analysis of the mineralogy of the sediments indicates that the material above the unconformity is enriched in minerals that are the products of a more intense weathering environment than those deeper in the profile. Oxygen-isotope ratios of ground ice in the sediments suggest the presence of two genetically distinct ice units above and below the unconformity. An average rate of upward permafrost growth in this area of 0.1–0.2 mm year−1 is calculated for the period since the climatic optimum.
Using discriminant function analysis to identify Holocene tephras based on magnetite composition: a case study from the Sunwapta Pass area, Jasper National Park
Authors: Beaudoin A. B. , King R. H.
Published: April 2011

The magnetite composition from three sets of samples of Mazama, St. Helens set Y, and Bridge River tephras from Jasper and Banff national parks are used to test whether discriminant function analysis can unambiguously distinguish these tephras. The multivariate method is found to be very sensitive to the change in reference samples. St. Helens set Y tephra is clearly distinguished. However, discrimination between Mazama and Bridge River tephras is less distinct. A set of unknown tephras from the Sunwapta Pass area was used to test the classification schemes. Unknown tephras are assigned to different tephra types depending on which reference tephra set is used in the discriminant function analysis.
The Lillooet terraces of Fraser River: a palaeoenvironmental enquiry
Authors: Ryder June M. , Church Michael
Published: April 2011

The history of Holocene fluvial terraces was investigated by stratigraphic, morphological, and palaeohydrologic methods. The terraces were formed in glaciofluvial and glaciolacustrine sediments by the Fraser River: degradation alternated with episodes of stability and aggradation. The uppermost terraces, four nonpaired surfaces, were occupied by a braided river. Vertical stability was controlled either by the water and sediment discharge of the river or by backwater effects from downstream landslides. The lower terraces, two paired surfaces, and associated fluvial sediments provide evidence for at least two cycles of aggradation and downcutting. These can be attributed to the effects of landslides that occurred a short distance downstream. Climatic variations may also have influenced terrace formation, but direct evidence is lacking. Palaeohydraulic investigations based on gravel texture, terrace gradients, and geometry of palaeochannels provide results that although approximate, conform with conclusions based upon terrace morphology and stratigraphy.
Glacial geology and Quaternary marine stratigraphy of the Robeson Channel area, northeastern Ellesmere Island, Northwest Territories
Authors: Retelle Michael J.
Published: April 2011

Glacial and marine deposits associated with two phases of glaciation are exposed along a 60 km corridor on Ellesmere Island that borders Robeson Channel. The oldest sediments, tentatively dated at ≥ 70 000 BP, were deposited during a major advance of the northwest Greenland ice sheet across Robeson Channel. During subsequent retreat of this ice mass, glaciomarine sediments containing a High Arctic macro- and microfauna were deposited in the isostatic downwarp on Ellesmere Island. This marine unit was radiocarbon dated at 31 300 ± 900 and > 32 000 BP; mean aIle/Ile ratios are 0.218 ± 0.03 for the free fraction and 0.063 ± 0.011 for the total acid hydrolysate.The last ice advance (late Wisconsin – early Holocene) did not extend into the field area from either interior Ellesmere Island or northwest Greenland. The ice-marginal sea transgressed to the marine limit (~116 m) and overlapped the deposits of the previous maximum Greenland advance. Local plateau ice caps did, however, spill over into one major valley and delayed the establishment of the marine limit in this location. Radiocarbon dates on the Holocene marine limit shorelines indicate initial emergence between 8000 and 8600 BP. A mean aIle/Ile ratio of 0.037 was found for the total acid hydrolysate; aIle was undetectable in the free fraction of the Holocene shells.The Holocene and pre-Holocene glacial and marine chronologies in the Robeson Channel area are similar to chronologies demonstrated from other locations in Arctic regions. Tentative correlations based upon aminostratigraphy suggest that the field area has remained, for the most part, ice free since at least 70 000 BP.
Triassic olivine-normative diabase from Northumberland Strait, eastern Canada: implications for continental rifting
Authors: Pe-Piper Georgia , Jansa Lubomir F.
Published: April 2011

Two intervals of mafic igneous rocks were encountered within a Silurian to Carboniferous sequence in an exploratory offshore well located in the Gulf of St. Lawrence, eastern Canada. Geochemical and radiometric analyses show that the lower mafic rocks are Early Silurian continental tholeiite lavas, with their radiogenic clock thermally reset during the Late Devonian. The upper igneous interval consists of several dikes of high-alumina diabase characterized by flat, relatively unenriched REE spectra and a positive Eu anomaly. This diabase resembles olivine tholeiites. Two K/Ar dates suggest a Late Triassic age for these intrusions. The dike composition differs from that of known Late Triassic and Early Jurassic continental tholeiites nearby in Nova Scotia, which are associated with a late stage of continental rifting. The Triassic – Early Jurassic igneous activity shows a pattern of geochemical evolution that we relate to mantle upwelling.
Petrochemistry and tectonic significance of Carboniferous volcanic rocks in New Brunswick
Authors: Fyffe L. R. , Barr S. M.
Published: April 2011

Carboniferous volcanic rocks from the New Brunswick Platform in the Maritimes Basin are divided into three age groups. Late Tournaisian to early Visean volcanic rocks are tholeiitic basalts and andesites that, in southern New Brunswick, are inter-bedded with abundant calc-alkalic rhyolite. Late Visean to Namurian volcanic rocks consist of an interbedded sequence of alkalic basalts and trachyandesites. Late Westphalian volcanic rocks change in composition up section from trachyte to peralkalic rhyolite. All three age groups display petrochemical features indicative of an intraplate tectonic setting. The volcanic geochemistry is consistent with the development of the Maritimes Basin either as a failed rift formed along the margin of a late Paleozoic ocean or as a rhomb graben formed within a transcurrent zone; the former model is preferred. The change in basaltic composition from tholeiitic to alkalic apparently coincided with a decrease in rate of extension between the Tournaisian and Namurian. Local peralkalic volcanism occurred during regional sagging of the basin as extension ceased and basement rocks cooled in the Late Carboniferous.
The Early Silurian brachiopod Pentameroides from the Hudson Bay Lowlands, Ontario
Authors: Jisuo Jin , Copper Paul
Published: April 2011

Reexamination and serial sectioning of the type material of Reticularia septentrionalis Whiteaves 1904 and Meristina expansa Whiteaves 1904, from the Silurian (upper Llandovery) Attawapiskat Formation, Ekwan River, Hudson Bay Lowlands, indicate that they belong to the same species and that they can be assigned to the genus Pentameroides. These described species are also identical to Sapelnikovia [=Reveroides] norfordi Boucot and Johnson 1979, from the same formation on the Attawapiskat River nearby. All three species are thereby assigned to a single species, Pentameroides septentrionalis. The inflated shell of this species ranges from smooth and nonlobate to bisulcate–bilobate and rarely weakly trisulcate. This morphology is thereby viewed as a species-specific character, leading to the conclusion that Reveroides Sapelnikov 1976 is probably a junior synonym of Pentameroides.
Nd evidence for extensive Archean basement in the western Churchill Province, Canada
Authors: Frost C. D. , Burwash R. A.
Published: April 2011

To determine the extent of reworked Archean crust in the western Churchill Province, we have examined Sm–Nd crustal residence ages of basement cores in southern Alberta and southwestern Saskatchewan along with crustal residence ages calculated for other Sm–Nd data available from the Churchill Province. The deep drill hole samples from the Interior Platform give Sm–Nd crustal residence ages that average 2.8 Ga. Granulites from northeastern Alberta and composite gneisses from northern Saskatchewan also provide Archean crustal residence ages. These data demonstrate that the presence of reworked Archean crust in the western Churchill Province is more widespread than has been confirmed previously. We suggest that Sm–Nd crustal residence ages are valuable estimates of crust formation times, especially in orogenic areas where other isotope systems have been disturbed.
Early Cretaceous gold–silver mineralization in the Sylvester allochthon, near Cassiar, north central British Columbia
Authors: Sketchley Dale A. , Sinclair A. J. , Godwin C. I.
Published: April 2011

K–Ar dates on sericite from several gold–silver bearing white quartz veins in the Cassiar area indicate that mineralization occurred in the Early Cretaceous at about 130 Ma. Thus, these veins predate the mid-Cretaceous Cassiar batholith and Late Cretaceous and early Tertiary plutons in the immediate area. The Early Cretaceous date probably represents either a thermal precursor to emplacement of the Cassiar batholith or a structurally related event associated with allochthonous emplacement of the Sylvester Group. Either of these events may have caused circulation of the meteoric fluids responsible for the veins.
The late Wisconsinan olistostrome of the lower Coppermine River valley, Northwest Territories
Authors: St-Onge Denis A. , Lajoie Jean
Published: April 2011

The late Quaternary olistostrome exposed in the lower Coppermine River valley fills a paleovalley that ranges in apparent width from 150 to 400 m and was cut into Precambrian bedrock before the last glaciation. The olistostrome is here named the Sleigh Creek Formation. The coarse fraction of the formation is matrix supported; beds are massive or reversely graded and have sharp, nonerosive contacts. These characteristics suggest deposition of the coarse fraction by debris flows. The olistostrome sequence is bracketed by, and wedged into, a marine rhythmite sequence, which indicates that deposition occurred in a marine environment.About 10 500 years BP glacier ice in the Coronation Gulf lowland dammed the valley to the south, which was occupied by glacial Lake Coppermine. Sediments accumulated in this lake in a 30 m thick, coarsening upward sequence ranging from glaciolacustrine rhythmites of silt and fine sand at the base to coarse sand alluvium, and deltaic gravels at the top. As the Coronation Gulf lowlands became ice free, the Coppermine River reoccupied its former drainage course to the north. The steep south to north gradient and rapid downcutting by the river through the glacial lake sediments produced unstable slope conditions. The resulting debris flows filled a bedrock valley network below the postglacial sea level, forming the diamicton sequence.The interpretation of the Sleigh Creek Formation raises questions concerning silimar diamicton deposits usually defined as "flowtills." More generally, the results of this study indicate that care must be used when attempting paleogeographic reconstructions of "glaciogenic" deposits in marine sequences in any part of the geologic record.
Subaqueous morphology and slope processes in a fjord delta, Bella Coola, British Columbia
Authors: Kostaschuk R. A. , McCann S. B.
Published: April 2011

An analysis of the subaqueous morphology of the Bella Coola delta, British Columbia, based on fathometer profiles, seismic and sidescan sonar surveys, gravity cores, and bottom grabs, defines a proximal, sandy delta front and a distal silt–clay prodelta. The former extends 3 km offshore to water depths of 275 m; the latter, 3 – 15 km down fjord to a depth of 550 m. Large chutes, succeeded downslope by depositional zones, characterize the delta front. Deep-seated rotational slides occur in the proximal part of the prodelta, indicating that the delta front and prodelta consist of separate mass-movement systems.
A rock avalanche triggered by the October 1985 North Nahanni earthquake, District of Mackenzie, N.W.T.
Authors: Evans S. G. , Aitken J. D. , Wetmiller R. J. , Horner R. B.
Published: April 2011

A major rock avalanche (estimated volume, 5–7 × 106 m3) was triggered by the October 1985 North Nahanni earthquake (Ms = 6.6). The landslide is located at 62.27°N, 124.18°W, 23 km southwest of Carlson Lake, in an uninhabited part of the District of Mackenzie, N.W.T. It occurred within 10 km of the epicentre. The rock avalanche detached from the northeast flank of a ridge located along the axis of the English Chief Anticline and involved massively bedded limestones of the Middle Devonian Nahanni Formation. Whilst most of the landslide mass was deposited at the foot of the original slope, a mobile tongue of debris turned at right angles to the direction of initial sliding and travelled down valley, coming to rest on a slope of about 5°. The distal margin of the mobile tongue is approximately 1.55 km from the top of the rupture surface. The fahrböschung of the landslide is estimated to be 14.5°, and the rock avalanche exhibits exceptional mobility in relation to its volume. The rupture surface is well exposed and is a combination of planar structural elements, viz. a bedding surface and a steeply dipping fault plane. The marked streaming behaviour in the mobile tongue raises the question of a possible link between this phenomenon and intense strong ground motion during the earthquake.
Grenvillian basement in the northern Cape Breton Highlands, Nova Scotia
Authors: Barr Sandra M. , Raeside Robert P. , van Breemen Otto
Published: April 2011

The northernmost Cape Breton Highlands are underlain by the Blair River Complex, a distinctive assemblage of basement rocks including felsic and mafic gneisses, foliated gabbroic to granitic rocks, anorthosite, and foliated and unfoliated varieties of syenite. Major faults and mylonite zones separate the complex from schists, gneisses, and granitoid rocks typical of the rest of the Cape Breton Highlands. U–Pb dating of zircon from the Lowland Brook syenite of the Blair River Complex indicates a metamorphic age of [Formula: see text] and an igneous age of 1100–1500 Ma. These ages and the distinctive rock assemblage allow the Blair River Complex to be correlated with the Grenvillian rocks in the Long Range Inlier and Indian Head Range Complex of western Newfoundland. This is the first confirmed report of Grenvillian basement in Cape Breton Island, and it places new constraints on correlations between Newfoundland and the northern mainland Appalachians.
Interplay between folding and ductile shearing in the Proterozoic crust of the Muskoka – Parry Sound region, central Ontario
Authors: Schwerdtner W. M.
Published: April 2011

Grenville gneiss of the central Georgian Bay region was subjected to ductile deformation that produced narrow mylonite zones as well as three sets of superimposed folds differing greatly in structural signature, size, and orientation. Some mylonite zones are concordant to gneissosity and are repeatedly folded, others cut gneissosity and postdate the folding. Gneissosity was generated as a regionally subhorizontal feature, either by crustal thinning or, like the early mylonite zones, by low-angle reverse shearing. An attempt is made to account for the initially subhorizontal gneissosity, the mylonite zones, and the folds in a regime of large-scale reverse shearing that strikes parallel to the Grenville Front.Upright northwest–southwest to north–south buckle folds dominate the map pattern and are subperpendicular to the reverse Grenville Front boundary fault. These set-2 folds cannot be attributed to reverse simple shearing but require a large component of east–west compression. Such stress could have been generated in a northwest–southeast zone of sinistral ductile shear caused by temporary locking of the southern segment of the Grenville Front boundary fault (now under Lake Huron).All structural facts can be explained without large differential translations of crustal slices. For example, most discordances in the regional gneissosity pattern could have been created by décollement and repeated buckling. Detailed geobarometry and petrologic studies may be required to settle the question of large-scale thrusting within the Grenville gneiss terrane.
Deep crustal structure and evolution of the rifted margin northeast of Newfoundland: results from LITHOPROBE East
Authors: Keen C. E. , Stockmal G. S. , Welsink H. , Quinlan G. , Mudford B.
Published: April 2011

As part of the LITHOPROBE East project, a marine deep seismic reflection line was run in 1984 across the continental margin northeast of Newfoundland. The seismic data define reflectors both within and below the sedimentary section. The deeper, intracrustal reflectors help determine the nature of extensional tectonics and associated sedimentary basin evolution on the rifted margin. The line also crosses the ocean–continent transition and helps define structure in that region. Interpretation of the seismic data shows that brittle extension of the upper crust was accommodated along at least one subhorizontal level of décollement. The most obvious style of deformation involves the shallowest level of décollement on which high-angle planar normal faults detach. A deeper level of décollement is inferred from the presence of low-angle listric normal faults penetrating the lower crust or deeper. There is no evidence for a unidirectional low-angle shear zone controlling extension. The seismic data are used to constrain a depth-dependent numerical model of extension. Best-fit estimates of the basin subsidence history support a model in which there are several episodes of stretching and in which there is significantly more stretching in the lower lithosphere than in the upper lithosphere. At the ocean–continent transition, the oceanic crust appears to thicken as it dips beneath the rifted continental crust. This may result from the production of basaltic magma and its migration to crustal levels during rifting.
Faunal associations of the Middle Jurassic ammonite genus Macrocephalites in Kachchh, western India
Authors: Krishna Jai , Westermann G. E. G.
Published: April 2011

New collections of Macrocephalitinae from the ?Upper Bathonian – Lower Callovian of Kachchh (Cutch olim) make it possible to discern six successive taxonomically distinguishable faunal associations. These are, from above, (6) M. semilaevis association, (5) M. formosus association, (4) M. dimerus association, (3) M. elephantinus association, (2) M. madagascariensis association, (1) M. triangularis association.Of these, Nos. 1, 4, and 6 formed the bases of the M. triangularis, M. dimerus, and M. semilaevis biozones respectively. The majority of the 19 nominal species and 6 genera in the literature on Kachchh may be condensed into only 6 dimorphic species of undivided Macrocephalites.
Stress drop estimates for some aftershocks of the Ometepec, Guerrero, Mexico, earthquake of June 7, 1982
Authors: Rebollar Cecilio J. , Alvarez Rosa M.
Published: April 2011

Brune's stress drop, apparent stress, and arms stress drop are estimated at a single station for 25 aftershocks of the Ometepec earthquakes (Ms = 6.9 and Ms = 7.0). The arms stress drops and apparent stresses are systematically smaller than Brune's stress drops. Stress drops from the root mean square of acceleration and apparent stress range from 0.01 to 10.2 bars (1 bar = 100 kPa) except for two values (21.4 and 33.0 bars). On the other hand, Brune's stress drops range from 0.6 to 239 bars. Seismic moments ranging from 0.5 × 1019 to 289 × 1019 dyn∙cm (1 dyn∙cm = 10 μN∙cm) were estimated for events with coda magnitudes between 0.6 and 2.2. Values of radiated seismic energy calculated by integration of the displacement spectra range from 2.5 × 1012 to 2.3 × 1016 dyn∙cm. The fmax values lie between 16 and 30 Hz. Seismic coda wave attenuation measured on narrow band-pass-filtered seismograms show a linear dependence of the seismic quality factor of the form [Formula: see text] in the range of frequencies from 3 to 24 Hz.
Thermoluminescence properties and age estimates for Quaternary raised marine sediments, Hudson Bay Lowland, Canada
Authors: Forman S. L. , Wintle A. G. , Thorleifson L. H. , Wyatt P. H.
Published: April 2011

Thermoluminescence (TL) analyses of Quaternary nearshore marine sediments from the Hudson Bay Lowland revealed relatively high light emissions and linear growth curves to at least 400 Gy above the natural dose. Initial results indicate that anomalous fading may be circumvented by a preheating at 150 °C for 16 h without substantial thermal draining of stable TL components. Both the total bleach method with unfiltered sunlamp light and the partial bleach method with light blocked below 400 nm resulted in overbleaching and thus overestimates of age. A TL age estimate of 5.3 ± 0.8 ka on the Holocene control sample, similar to the radiocarbon age, was obtained using the partial bleach method with light blocked below 540 nm. This same method yielded an average TL age estimate of 73 ± 10 ka for a Pleistocene unit, which corresponds to the amino-acid-based age estimate of ca. 76 ka. The agreement of the two age estimates is encouraging, since both methods rely on separate assumptions that have not been independently verified.
Essai de corrélation stratigraphique et structurale à l'est de Val-d'Or: implication pour la prospection aurifère du secteur
Authors: Marquis Robert , Goulet Normand
Published: April 2011

Stratigraphic and structural relationships show that the Trivio and Garden Island sedimentary groups could be lateral equivalents. The ubiquitous presence of shear zones between the sedimentary (Trivio and Garden Island) and volcanic (Kinojévis and Malartic) groups indicates that these contacts are tectonic and not stratigraphic. Moreover, the shearing along the Malartic–Trivio contact is located along the extension of the Larder Lake – Cadillac fault zone and could be its equivalent east of Val-d'Or, Quebec.Three major periods of deformation have been recognized in the field. The main east–west deformation, D2, has produced isoclinal folds inclined to the southwest and plunging 60° to the northeast. The axial-plane schistosity associated with D2 is responsible for the regional tectonic grain. Its orientation, 290°/70°, closely parallels the shearing direction along the major volcanic–sedimentary contacts. At Chimo mine, on a mesoscopic scale, the isoclinal D2 folds refold D1 structures, producing interference patterns intermediate between types 2 and 3. On a regional scale the D1 folds do not affect the lithologic pattern.A late deformation, D3, becomes progressively more noticeable toward the Grenville Front. Folds related to this third phase are inclined toward the northwest and plunge to the northeast. The orientation of the fracture cleavage associated with this deformation is 040°/60°. The proximity of the Grenville Front, north of Lake Matchi-Manitou, is shown by strike faults oriented northeast–southwest. The sinistral movement of these faults was determined using a banded iron formation as marker horizon.All gold exploration criteria suggest that the study area is a favourable target for gold exploration.
Geochemistry and origin of Archean felsic metavolcanic rocks, central Noranda area, Quebec, Canada
Authors: Ujike Osamu , Goodwin A. M.
Published: April 2011

Felsic magma petrogenesis was studied by analyzing 24 stratigraphically controlled Archean andesite-to-rhyolite lava flows of both tholeiitic and calc-alkalic affinity from the upper Noranda Subgroup, Quebec, using instrumental neutron activation and X-ray fluorescence techniques. The lavas have moderate values of [La/Yb]N (0.9–3.8) and low values of 100 × Th/Zr (~1). According to calculations following batch partial melting and Rayleigh fractional crystallization models, both the calc-alkalic and tholeiitic felsic volcanic rocks are probably products of shallow-level fractional crystallization of mafic parental magmas formed respectively by lower (~7 % for calc-alkalic) and higher (~14% for tholeiitic) degrees of partial melting of a primitive mantle source.Contribution to the magma genesis from plausible crustal materials was negligible. A back-arc-type diapirism is geochemically suggested for the tectonic model of origin of Noranda felsic magmas, in conformity with geological observations. Felsic volcanic rocks with compositions analogous to the studied samples exist in several other Archean terrains of the Canadian Shield, suggesting thereby that the late Archean sialic crust was at least in part produced by volcanic rocks ultimately derived from the primitive mantle.
A new specimen of giant land tortoise (Geochelone sp.) from the Wood Mountain Formation (Middle Miocene) of Saskatchewan
Authors: Holman J. A. , Tokaryk Tim T.
Published: April 2011

A relatively complete shell of a giant land tortoise, Geochelone sp., from the Middle Miocene Wood Mountain Formation of Saskatchewan further documents records heretofore based on fragments. The occurrence of this tortoise in fossil deposits in Canada has previously been interpreted as indicating a subtropical climate in the Middle Miocene.
Oxygen-18 and carbon-13 in the carbonates of the Salina formation of southwestern Ontario
Authors: O'Shea K. J. , Miles M. C. , Fritz P. , Frape S. K. , Lawson D. E.
Published: April 2011

The oxygen and carbon isotopic composition of the carbonates of the Upper Silurian Salina formation of the Michigan Basin was investigated to aid in interpretation of depositional environments.13C results indicate that a change from generally anoxic bottom conditions to oxic conditions occurred during deposition of the B evaporite unit. The organic-rich A carbonate units were deposited in a shallow-water, evaporitic setting, most likely adjacent to a sabkha-type environment. A positive water balance maintained the anoxic conditions and buffered the carbon isotopes.Above the B evaporite, the isotopic composition suggests that the development of a similar depositional environment, a subaerial prograding sabkha, occurred over wide areas of the basin.18O results support the conclusion that Silurian oceans were depleted in 18O with respect to modem oceans by 5–6‰.
The Alekseev–Mikhailenko method applied to P–SV wave propagation in an elastic medium
Authors: Pascoe L. J. , Hron F. , Daley P. F.
Published: April 2011

The Alekseev–Mikhailenko method (AMM) is the name given to a series of algorithms that use one or more finite spatial transforms to reduce the dimensionality of a wave-propagation problem to that of one space dimension and time. This reduced equation is then solved using finite-difference techniques, and the space–time solution is recovered by applying inverse finite spatial transform(s). In this paper the elastodynamic wave equation that governs the coupled P–Sv motion in an isotropic, vertically inhomogeneous elastic half space is investigated using the AMM. Two types of impulsive body forces that may be used to excite the medium are examined, as is the problem of obtaining accurate transformed finite-difference analogues at the free surface. The second of these is accomplished by introducing the boundary conditions that the shear and normal stress must vanish here and by incorporating their transforms into the transformed elastodynamic equations. The stability criterion for the explicit finite-difference method is given cursory treatment, as detailed discussion of this aspect may be found in many texts that deal with the subject of finite differences.A coal-seam model (two thin, low-velocity layers embedded in a half space) illustrates the method. Both horizontal and vertical seismic traces are computed for this model and the results examined in relation to other seismic-modelling techniques.
Physical volcanology of the footwall rocks near the Mattabi massive sulphide deposit, Sturgeon Lake, Ontario
Authors: Groves D. A. , Morton R. L. , Franklin J. M.
Published: April 2011

Subaerial and shallow subaqueous mafic hyalotuffs, lava flows, and flow breccias, felsic lava flows, and pyroclastic flows and falls form a 2 km thick succession beneath the Mattabi massive sulphide deposit. The lowermost 800 m of section comprises massive to amygdaloidal mafic flows and flow breccias interlayered with repetitive sequences of thinly bedded felsic tuff: pillow lavas and hyaloclastites are absent. Amygdaloidal felsic lavas overlie the mafic flows and are locally capped by coarse explosion breccia. This breccia is believed to represent the start of mafic hydrovolcanism, which produced ash falls, surges, and flows. These pyroclastic deposits formed thin- to thick-bedded hyalotuffs that contain highly vesicular and quenched juvenile and accessory lithic fragments. Periods of water influx probably led to the construction of a tuff cone, which represents a submergent hydrovolcanic cycle.In the Mattabi area, pyroclastic flow deposits form the immediate mine footwall strata and include (i) massive basal beds and overlying bedded ash tuffs and (ii) massive pumiceous units. These deposits overlie and, to the west in the Darkwater Lake area, are intercalated with the mafic hyalotuff sequence. The morphology of the footwall volcanic rocks indicates that the Mattabi and the F-zone massive sulphide deposits formed in a shallow subaqueous environment.
Structural patterns and tectonic evolution of supracrustal domains in the Archean Slave Province, Canada
Authors: Fyson W. K. , Helmstaedt H.
Published: April 2011

A new plate-tectonic model accounts for lithological relations and regional structural patterns in late Archean supracrustal domains of the Slave Province. Multiple dykes and pillowed mafic flows, most common in the western part of the province, suggest sea-floor spreading. The mafic volcanics, lying in narrow homoclinal belts stratigraphically below more extensive turbidites, are viewed as megaxenolithic remnants of oceanic crust preserved on the periphery of granitoid plutons and blocks of sialic crust. Closure of an oceanic basin was marked by emplacement of the granitoid plutons and coeval felsic volcanics, the latter predominating over mafic volcanics in northeastern domains. The felsic calc-alkaline magmas may have risen from a shallow-dipping subduction zone. Westerly verging folds, westerly convex fold arcs, and inclinations of later foliations, particularly in lower level rocks of higher metamorphic grade, are in accord with underthrusting to the east. The zone of underthrusting shifted progressively westward, and calc-alkaline magmatism swept across the western part of the province. Plutons followed crustal fracture systems, some of which were inherited from initial rifts, producing a rectilinear zigzag pattern of contacts between plutons, and mafic volcanics. The fracture systems and rising plutons redirected stresses, resulting in distinctive sets of regional and local foliations that reflect crustal compression only indirectly related to the sense of subduction.
Palynology of Maastrichtian and Paleocene rocks, lower Colville River region, North Slope of Alaska
Authors: Frederiksen N. O. , Ager T. A. , Edwards L. E.
Published: April 2011

Outcrops of Maastrichtian rocks are rare on the North Slope of Alaska, and it is even more unusual to find outcrops of Maastrichtian and Paleocene age in the same vicinity. In general, Late Cretaceous and Paleogene rocks have not been well dated in published papers pertaining to northern Alaska. In this article, we describe palynomorph assemblages from 20 outcrop samples taken from nine localities along the lower Colville River and nearby areas. The latest Cretaceous palynomorph assemblages that are from marine rocks contain late Campanian or Maastrichtian dinoflagellate cysts; however, these cysts and other marine fossils are absent from the Tertiary samples, indicating that the Tertiary strata are nonmarine. Our latest Cretaceous and early Tertiary samples contain abundant spores and pollen grains and can be readily dated by reference to well-known pollen assemblages from the northern Great Plains and northwestern Canada. By dating each sampled outcrop, we can approximate the position of the Cretaceous–Tertiary boundary in the study area. Outcrop samples near the boundary are too widely separated stratigraphically to permit us to determine whether or not an unconformity exists at the boundary in the study area. Using spores, pollen grains, and dinoflagellate cysts, we date the samples below the Cretaceous–Tertiary boundary as being of approximately mid-Maastrichtian age and the samples above the boundary as being undifferentiated Paleocene in age. On the North Slope, as in regions to the east and south, the Maastrichtian pollen assemblages represent a different kind of flora and vegetation than the Paleocene assemblages. The Maastrichtian assemblages have moderately high diversities of angiosperm pollen taxa, most of which were probably insect pollinated. In contrast, the Paleocene assemblages have low diversities of angiosperm taxa, and many of these taxa were probably wind pollinated. Differences between the mid-Maastrichtian and Paleocene assemblages may have been caused at least in part by climatic changes but may also have been caused by the effects of a hypothesized bolide impact at the end of the Maastrichtian for which there is increasing evidence.
Geology of part of a long-lived dynamic plate margin: the coastal cordillera of north-central Chile, latitude 30°51′–31°S
Authors: Irwin James J. , García Carlos , Hervé Francisco , Brook Maureen
Published: April 2011

A complex composed of ultrabasic and basaltic lavas, chert, arkose, and conglomerate was assembled in the coast of north-central Chile (lat. 30°30′–31°S) prior to 200 Ma. The character of, and relationships between, the rock formations exposed here are consistent with an autochthonous evolution of this part of Chile in the last 200 Ma. Three major episodes of deformation and metamorphism have been observed in this area. The first episode (F1) produced a compositional layering (S1) and amphibolite-facies metamorphism coeval with the intrusion of an extensive igneous complex between 220 and 200 Ma. A second episode of deformation (F2) locally formed reverse faults and tight, recumbent folds in S1. Units in which F2 folds are well developed yield K–Ar and Rb–Sr ages between 163 and 140 Ma. At between 140 and 126 Ma, upright, open to tight folds (F3) formed with sharp hinges and axial planes that strike north and dip steeply east. Structures of similar age, style, and orientation have been reported as far south as Tierra del Fuego. The timing of the F3 deformation appears to correspond to the opening of the South Atlantic Ocean and accelerated westward motion of South America.
Geophysical interpretation of the geology of the northeast Gander Terrane, Newfoundland
Authors: Miller H. G.
Published: April 2011

New gravity data from the northeastern portion of the Gander Terrane of Newfoundland are analysed in association with existing gravity data. These are combined with the digitized and filtered aeromagnetic and geochemical data to produce an interpretation of the subsurface geology.Interpretation of these data suggests that there are two extensive areas underlain at depth by rocks similar to the Dunnage Terrane mafic and ultramafic rocks that outcrop at the Gander River ultrabasic belt. These regions of ultramafic and mafic rocks extend in two north–south belts throughout the study area, and both may have tongues continuing seaward beneath the Deadman's Bay pluton. The western belt, the Ocean Pond belt, probably consists of a series of granitic plutons underlain by mafic and ultramafic rocks. Geophysical modelling corroborates an earlier geological interpretation that the eastern belt, the Indian Bay Big Pond thrust belt, is a thrust sheet. The lateral extent of the thrust belt is accurately determined by new geophysical data. The presence of these two subsurface units composed of material similar to typical Dunnage Terrane rocks demonstrates that the Gander River ultrabasic belt is neither the most eastward extent of the Dunnage Terrane nor the sole thrust upon which Dunnage Terrane material was transported eastward. The two belts have associated diagnostic geochemical signatures and are bounded on the north and south by linear patterns in both the geophysical and geochemical patterns. The block defined by these geophysical and geochemical patterns is the same as that upon which the classic Gander Terrane was defined. The evidence presented in this paper suggests that this block may be allochthonous, which implies that the nature of the Gander Terrane may need to be reconsidered.
Biochronology of selected Bowser Basin strata; tectonic significance
Authors: Moffat I. W. , Bustin R. M. , Rouse G. E.
Published: April 2011

Recent evaluation and reinterpretation of fossil floral and faunal data more clearly define the ages of strata exposed in the Groundhog Coalfield and the surrounding Bowser Basin of north-central British Columbia. In the Groundhog Coalfield, Bowser Lake Group strata consist of an overall coarsening-upwards cycle divisible into four informal stratigraphic units, which are, from oldest to youngest, the Jackson, Currier, McEvoy, and Devils Claw units. The section has an unconformable relationship with underlying Bajocian Spatsizi marine shales, volcanics, and arenaceous sediments. Marine macrofossils indicate a Callovian to Oxfordian age for the Jackson unit. The fossil plant succession present in the overlying Currier unit indicates Late Jurassic affinities. Recent unpublished palynologic data from lower McEvoy rocks in the northern Groundhog Coalfield suggest a Barremian age. The palynoassemblage present in the lower Devils Claw unit in the central part of the Groundhog Coalfield suggests a late middle Albian age.Rocks of the Sustut Group have an angular unconformable relationship with underlying Bowser Lake Group strata near the eastern margin of the Bowser Basin. The palynoassemblage present in Sustut Group rocks from the southern Sustut Basin suggests a Campanian to Maastrichtian age range, in contrast to a probable late Albian to Campanian age range for the northern Sustut Basin and a middle to late Albian age from Sustut Group outliers present within the northern Bowser Basin. Within the Groundhog Coalfield, Devils Claw strata have a conformable or paraconformable relationship with underlying Bowser Lake Group strata.Regional discrepancy in the age and geometry of the sub-Sustut unconformity is attributed to a time-transgressive unconformity that resulted from cratonward advance of an isostatically induced peripheral bulge. Age and contact relationships suggest that deformation in the Bowser Basin and surrounding Sustut Basin must have spanned the time period that corresponds to a second uplift pulse of the Columbian orogen (Aptian to early Cenomanian) and the uplift pulse related to the Laramide orogen (Campanian to Maastrichtian).
Structural evolution of basement gneisses and Hadrynian cover, Bulldog Creek area, Rocky Mountains, British Columbia
Authors: McDonough Michael R. , Simony Philip S.
Published: April 2011

Two gneiss bodies are contained in thrust sheets on the west edge of the Rocky Mountain Main Ranges near Valemount, British Columbia. The Bulldog Gneiss comprises Aphebian or older paragneiss and amphibolitic gneiss intruded by Aphebian orthogneiss sheets. The Yellowjacket Gneiss is granodioritic orthogneiss of unknown age. Both gneiss bodies are basement highs with thin Hadrynian metasediment cover sequences. The cover sequences are assigned to the lower Miette Group and are correlated with Horsethief Creek Group.Internal shortening of gneiss thrust sheets is expressed by recumbent folding and stacking of thin thrust sheets of gneiss and cover. The Bulldog Gneiss and its cover were carried on the postmetamorphic Purcell Thrust. The Yellowjacket Gneiss and its cover were carried on the pre- to synmetamorphic Bear Foot Thrust. Northeast and northwest displacement is documented on the moderately southwest-dipping Bear Foot Thrust, and a dextral oblique-slip – thrust model is proposed to explain the duality of thrust and dextral strike-slip kinematic indicators in mylonite from the fault. An estimate of shortening in the fore-land suggests that basement thrust sheets were translated more than 200 km to the northeast.Correlation of gneisses and cover with the westerly adjacent Malton Gneiss and its cover precludes major dextral strike-slip motion on the Southern Rocky Mountain Trench (SRMT) during and after thrusting. The SRMT was the locus of post-thrusting and postmetamorphic, Eocene(?), brittle, west-side-down, normal faulting.