bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative geochemistry and petrology of Triassic basaltic rocks from the Taku terrane on the Chilkat Peninsula and Wrangellia
Authors: Davis Alicé , Plafker George
Published: April 2011

Upper Triassic metabasalt from the Chilkat Peninsula in southeastern Alaska is lithologically similar to the Middle and (or) Upper Triassic Nikolai Greenstone from the Wrangell Mountains, east-central Alaska. Both basaltic sequences show comparable petrologic and geochemical features. The informally designated Chilkat metabasalt, which forms part of a Triassic sequence between the Denali fault and the Chilkoot lineament, is included in the Taku terrane, whereas the Nikolai Greenstone characterizes the allochthonous Wrangellia terrane. The Chilkat metabasalt consists mostly of massive to inconspicuously layered flows with well developed pillow structures at the top of the section; the sequence may reach a total thickness of 3000 m. The metabasalt is predominantly amygdaloidal and contains secondary minerals typical of greenschist-facies metamorphism. The Nikolai Greenstone is a widespread, mostly subaerial but locally pillowed, amygdaloidal basaltic sequence that reaches a total thickness of more than 3500 m; it is commonly less metamorphosed than the Chilkat metabasalt and contains secondary minerals typical of zeolite-facies to very low greenschist-facies metamorphism. Both the Chilkat and Nikolai basaltic rocks are predominantly tholeiitic. The major-element compositions of both sequences are very similar and cluster within a narrow range. The trace-element data for both sequences suggest a composition similar to the high-magnesian Columbia River flood basalts. Sediments associated with the Chilkat and Nikolai basaltic rocks share gross lithologic features and a similar depositional environment, even though the upper part of the Chilkat sequence appears to be a more offshore facies. The petrologic and geochemical data are compatible with the inference that the Taku terrane may have been coextensive with Wrangellia during the Late Triassic but has subsequently been laterally offset by dextral movement on the Denali fault.
Origin and magnetic fabric of glacial varves, Nottawasaga River, Ontario, Canada
Authors: Gravenor C. P. , Coyle D. A.
Published: April 2011

An examination of the glacial varved clays that crop out in the banks of the Nottawasaga River, Ontario, shows that both the silt and clay layers are composed of sublaminae.An analysis of the magnetic fabric and remanent magnetization of the varves shows that the current directions are the same for the clay and silt layers and that the magnetic fabric in the clay layer was not influenced by the Earth's magnetic field. This indicates that bottom currents were active during the winter period and were of sufficient strength to align the particles of magnetite parallel to the current directions. This conclusion is not unique to the Nottawasaga varves but serves to illustrate that the conceptual model of glacial varve deposition requires modification.
On the origin of the Oak Ridges Moraine, southern Ontario
Authors: Chapman L. J.
Published: April 2011

Widespread occurrences of stratified silt and clay have been found under the surface sands on the crest of the Oak Ridges Moraine between Stouffville and Pontypool, Ontario. It is suggested that the most likely explanation for the submergence of that part of the moraine is that the Lake Ontario ice lobe was still overriding the Niagara Escarpment at the time, holding standing water in the area between the southern and northern ice lobes and the escarpment. A stream channel over the escarpment, extending from northeast of Cheltenham to Acton and beyond, may have served as the outlet. This sill is high enough to have held water over the above-mentioned silts and clays. It is of interest that this outlet channel led eventually to glacial Lake Whittlesey, indicating a correlation.
Pétrologie et signification géotectonique des plutonites de Kambusi (sud Kivu, Zaïre)
Authors: Rumvegeri Boneza R. , Caron Jean-Paul H. , Kampunzu Ali B. , Lubala Ruananza T. , Vellutini Pierre J.
Published: April 2011

The massif of Kambusi, located about 30 km northwest of Bukavu, is made up of two intrusive plates: microgranite to the south and microsyenite to the north. These plates were emplaced during the Cambrian.The microsyenite is characterized essentially by the association of quartz, perthites, albite + K-feldspar, olivine, hedenbergite, edenitic hornblende, iron-rich biotite, ilmenite, and fluorine. The microgranite is distinguishable from the microsyenite by an absence of olivine, pyroxene, and fluorine, a relative richness of quartz and amphibole, and a scarcity of feldspar in the modal composition.These magmas are typically alkaline (some rocks show a hyperalkaline tendency) and were emplaced at a shallow depth under low values of [Formula: see text] and [Formula: see text] and high T (> 890 °C). They are considered to mark the relaxation stage typifying the change of tectonic regime that took place at the end of the Panafrican.
Pollen analysis of postglacial sediments from Eildun Lake, District of Mackenzie, N.W.T., Canada
Authors: Slater Donald S.
Published: April 2011

Sediment from Eildun Lake, located at 63°8.6′N, 122°46.5′W in the northern boreal forest, was cored to a depth of 268 cm and analyzed for pollen content. Pollen percentages and 14C dates suggest a vegetational sequence extending back over 11 000 years. The sequence begins with a discontinuous herb tundra dominated by Artemisia and Gramineae. This was succeeded by a shrub tundra dominated by dwarf birch and willow. Poplar had invaded by approximately 10 700 BP to form a dwarf birch – poplar groveland or forest tundra. Between approximately 10 300 and 7510 BP spruce replaced poplar as the dominant tree, although still forming a forest tundra. Boreal forest, including tree birch and alder, became established shortly after 7510 BP and has persisted since then with very little change. Pinus pollen has increased in percentage, particularly during the last 2400 years, reaching its Holocene maximum at the present day. The percentages attained indicate the presence of pine trees regionally though not in the near vicinity of Eildun Lake.
New geochronological information by Rb–Sr and U–Pb investigations from the pre-Alpine basement of Grande Kabylie (Algeria)
Authors: Bossière Gérard , Peucat Jean-Jacques
Published: April 2011

This study presents the first geochronological results, apart from previously obtained mica ages, from metamorphic basement complex occurring within the internal zone of the Alpine chain of Algeria. The Rb–Sr whole-rock and U–Pb zircon data reveal the existence of an episode of anatectic magmatism around 510 Ma ago that corresponds to late Pan-African orogenic events.A deep crustal fault is thought to represent a major phase of shearing associated with Hercynian blastomylonitic metamorphism and the production of granitic remelts at 271 ± 12 Ma. Reworking of an ancient basement is demonstrated by the presence of inherited radiogenic lead in zircons from lower Palaeozoic orthogneisses and metarhyolites: upper intercepts on concordia plots yield ages of 1950 ± 100 and 1321 ± 30 Ma, respectively. Apart from the dating results, which may provide new insight into the geological history of the region, this study also provides general implications for the interpretation of geochronological data in metamorphic and igneous formations.Firstly, the effect of the transformation of granite to orthogneiss appears to produce a dispersion of Rb–Sr analytical points between two apparent isochrons of 565 ± 50 and 465 ± 52 Ma. Such ages may also correspond to two separate groups of granitic protoliths that are difficult to distinguish in the field because of the superimposition of a gneissose fabric. In fact, the true emplacement age of these metagranites is given by the U–Pb zircon ages around 510 Ma. The Rb–Sr whole-rock systems of these orthogneisses have been opened during subsequent metamorphism, since model initial 87Sr/86Sr ratios calculated at 510 Ma are sometimes too low (< 0.700) to be explained by heterogeneity of the source materials.Secondly, the influence of fractional crystallization of a granitic melt on the behaviour of inherited zircon xenocrysts has been investigated. This involves the U–Pb study of further zircon separates from rocks having the same emplacement age but differing degrees of differentiation. An orthogneiss showing relative little magmatic differentiation (SiO2 = 65%) contains zircons that have a component of inherited radiogenic lead and that yield a lower intercept age of 506 ± 3 Ma. Two other orthogneisses showing far greater differentiation (SiO2 = 70 and 78%) contain zircons that lack any inherited radiogenic lead and that yield an upper intercept on concordia plots of 514 ± 18 Ma. This behaviour can be explained in the light of published experimental data on the dissolution of zircons in granitic liquids.
Seismic stratigraphy and structure of the east Canadian continental margin between 41 and 52°N
Authors: Parson L. M. , Masson D. G. , Pelton C. D. , Grant A. C.
Published: April 2011

The seismic stratigraphy of the eastern Grand Banks continental margin is examined, and a five-fold division of the sedimentary sequence overlying basement is proposed. Oceanic basement of Cretaceous age underlies the eastern part of the study area; to the west, continental basement ranging in age from Late Precambrian to ?Jurassic underlies the Grand Banks. The sediment units, ranging in age from Early Cretaceous to Recent, have been dated by extrapolation of both commercial and DSDP drilling results from the Grand Banks and from the formerly conjugate Iberian margin. Identification of oceanic magnetic anomalies in the Newfoundland Basin agrees with the proposed age of the two oldest, Early Cretaceous units.
Quartz-grain surface textures: evidence for a tropical climate during the Middle Pennsylvanian in eastern Canada
Authors: D'Orsay A. Murray , Poll H. W. van de
Published: April 2011

Scanning electron microscope examination of quartz grains separated from conglomerates in an alluvial fan sequence within the Pennsylvanian Fowler Head Formation of Nova Scotia revealed surface characteristics that are typical of those obtained from modern tropical environments. This evidence suggests that a similar tropical climate may have existed in eastern Canada during Middle Pennsylvanian time.
Accelerator radiocarbon date confirms early deglaciation of the Queen Charlotte Islands
Authors: Mathewes Rolf W. , Vogel J. S. , Southon J. R. , Nelson D. E.
Published: April 2011

Accelerator mass spectrometry was used to test whether part of eastern Graham Island was ice free at the height of late Wisconsin glaciation on mainland British Columbia. An accelerator radiocarbon date of 14 700 ± 700 years on a small twig conforms with two conventional dates that suggested that the Cape Ball region of Graham Island was deglaciated by about 15 000 radiocarbon years ago.
Radionuclide mobility in thucholitic hydrocarbons in fractured quartzite
Authors: Åberg G. , Löfvendahl R. , Nord A. G. , Holm E.
Published: April 2011

Radioactive hydrocarbons (thucholites) fill joints and fissures in Presvecokarelian quartzites around the town of Västervik, southeastern Sweden. Uranium series nuclides, including stable end members, and carbon isotopes have been measured in surface samples and in drill-core material originating down to 60 m below the surface. Uranium both is adsorbed onto noncrystalline hydrocarbonaceous material and forms different mineral phases. The amount of hydrocarbons and uranium rapidly decreases with depth: below 60 m the accumulations were too scanty for sampling. Uranium series nuclides show distinct gradients. The surface samples, with uranium contents up to 50 wt.%, have been enriched in uranium, lead, and particularly thorium in geologically recent time, probably during the last glaciation. Along the drill cores thorium has been immobile, whereas 226Ra and 222Rn have migrated. Uranium has been distinctly migratory at and close to the surface but more or less immobile below 20 m depth. Almost no foreign radioelements have been added to the examined mineralizations. The δ13C values of the examined hydrocarbons are −32 to −46‰ relative to PDB, with the lower values in the thicker hydrocarbonaceous masses at the surface. Because of complex open system behaviour, the age of the uranium accumulations is open to dispute. A Mesozoic age is favored here, but a Precambrian age cannot be ruled out.
Geology and geochemistry of the East Bull Lake intrusion, District of Algoma, Ontario
Authors: James R. S. , Born P.
Published: April 2011

The East Bull Lake intrusion is a layered basic lopolith of early Aphebian age that intrudes Archean basement rocks at the southern margin of the Superior Province. It contains at least two magmatic cycles. Cumulate olivine, plagioclase, and clinopyroxene form anorthosite, troctolite, and olivine gabbro–norite in the lower portion of each cycle. These rocks are overlain by two pyroxene gabbros–norites in which orthopyroxene (or pigeonite) joins augite and plagioclase as the major cumulate minerals. Molecular proportion ratio (MPR) variation diagrams support this interpretation of the petrology of the intrusion and show that the major cumulate rock types represent magmatic liquids formed sequentially by fractionation of the above-mentioned cumulate phases.Small-scale phase layering is common in the intrusion. Size-graded layers are absent, and cross-bedded and igneous lamination features are not common. We conclude that this scale of layering formed in a boundary layer along the floor of the intrusion as a result of variable nucleation of the cumulate minerals. Much thicker isomodal layers of rock form the main mass of the intrusion. They may have formed by a double diffusion process that caused the formation of a density-stratified magma chamber.
Offshore extensions of the Avalon Zone of Newfoundland
Authors: Miller H. G. , Goodacre A. K. , Cooper R. V. , Halliday D.
Published: April 2011

Gravity and magnetic data from the nearshore region of the Avalon Zone of Newfoundland provide evidence of the nature of a sedimentary basin immediately east of the Avalon Peninsula. The data also suggest a strong correlation between the arcuate magnetic patterns of the offshore portion of the Avalon Zone and the Precambrian mafic volcanics mapped onshore. The offshore basin is interpreted to have been formed by Precambrian block faulting and subsequently filled by sediments derived from surrounding paleotopographic highs. Two-dimensional gravity and magnetic modelling results suggest the presence of mafic material beneath the modelled 9+ km of sediment in the basin.
Jurassic–Cretaceous rock units along the southern edge of the Wrangellia terrane on Vancouver Island
Authors: Rusmore Margaret E. , Cowan Darrel S.
Published: April 2011

Rocks formerly mapped as Leech River Formation can be subdivided into two partly coeval rock units with completely different histories. The Upper Jurassic – Lower(?) Cretaceous Pandora Peak unit, which comprises black mudstone, terrigenous greywacke, radiolarian ribbon chert, green tuff, metabasaltic greenstone, minor pebbly mudstone, and a few blocks of limestone, was probably deposited in small basins on a continental margin. Local stratal disruption occurred before sediments were lithified. A static, high-pressure, low-temperature metamorphism produced lawsonite-bearing assemblages in metaclastic rocks. The Pandora Peak unit was originally coextensive with the Pacific Rim complex on western Vancouver Island and the Constitution formation in the San Juan Islands of Washington. The Leech River complex consists of foliated metasandstone, phyllite, and minor metabasalt of probable Jurassic–Cretaceous age. Multiple folding, transposition, and synkinematic greenschist- to amphibolite-facies metamorphism culminated about 40 Ma.The Pandora Peak unit is separated from crystalline rocks of the Wrangellia terrane by major faults. In southeast Victoria, partly retrograded amphibolites of the Wark–Colquitz complex overlie locally cataclastic lawsonite-bearing Pandora Peak rocks along the newly discovered Trial Islands thrust. A similar thrust separates the two units in Finlayson Arm, but near Port Renfrew the Pandora Peak terrane and crystalline West Coast complex are juxtaposed along the high-angle San Juan Fault. In each of these areas, emplacement of the Pandora Peak unit postdated the high-pressure (lawsonite-grade) metamorphism, which occurred between late Albian – early Cenomanian and Santonian–Campanian time (approximately 99–83 Ma). The Pandora Peak terrane was emplaced during a major Late Cretaceous or early Tertiary tectonic event that modified and probably truncated the southern margin of the Wrangellia terrane. Following this event the Leech River complex was faulted against the southern margin of the Pandora Peak terrane near Port Renfrew and in Goldstream Park in the Late Eocene or Early Oligocene.
Rb–Sr dating of the Bokan Mountain granite complex and its country rocks
Authors: Armstrong Richard Lee
Published: April 2011

Seven out of 11 whole-rock samples of the Bokan granitic complex give a Rb–Sr isochron date of 151 ± 5 Ma (Late Jurassic) as a minimum age for the complex. This result is discordant with published Early to Middle Jurassic K–Ar and U–Pb dates for the same unique peralkaline rock suite. A Late Jurassic age is tenable if excess radiogenic Ar and a trace of xenocrystic zircon are postulated to explain the previously reported results and the U–Pb data are reinterpreted to give an age between 156 ± 6 and [Formula: see text]. Granitic country rock for the complex is dated by Rb–Sr at 432 ± 19 Ma (Early Silurian), in agreement with published K–Ar dates.
Upper Paleozoic to lower Mesozoic strata and their conodonts, western Coast Plutonic Complex, British Columbia
Authors: Woodsworth G. J. , Orchard M. J.
Published: April 2011

Six lithologic units, including two newly named formations, were mapped on Randall, Dunira, and nearby islands. The islands are characterized by greenschist-facies metamorphism and westerly directed thrusting. The oldest unit is a Late Mississippian, massive limestone on Ducie Island. The Dunira Formation, composed of thin-bedded limestone and siltstone, is Early and Middle Pennsylvanian in age. It is unconformably overlain by limestone and dolomite of the Upper Triassic Randall Formation. The Randall Formation grades upwards into a green phyllitic unit of Late Triassic(?) age. Rhyolitic and more mafic volcanic rocks may represent a bimodal volcanic suite of Early Jurassic age, based on a U–Pb date of 188 Ma on zircons. These five units correlate with rocks in the Alexander Terrane in southeastern Alaska. The sixth and presumed youngest unit consists of flysch-like sedimentary rocks of probable Middle Jurassic to Early Cretaceous age that may correlate with rocks of the Gravina–Nutzotin belt. The three older units yielded 15 conodont genera from 29 localities. The 13 Paleozoic genera are described and illustrated.
Petrology and geochemistry of Cambrian volcanic rocks from the Avalon Peninsula, Newfoundland
Authors: Greenough John D. , Papezik V. S.
Published: April 2011

Middle Cambrian basaltic flows, lapilli tuffs, and their feeder pipes, on the Avalon Peninsula, Newfoundland, show high Nb/Y and low Zr/Nb ratios and high concentrations of incompatible elements, such as Nb and Zr, which are typical of alkaline rocks. The compositions of relict clinopyroxenes are consistent with these conclusions. Relatively low Mg′ values and low CaO and high TiO2 concentrations show that the flows represent evolved compositions. Petrographic evidence and trends in trace-element data indicate that the range of bulk-rock compositions in the feeder pipes can be related to precipitation of augite, plagioclase, and olivine as well as late removal of Fe–Ti oxides and apatite. The negative correlation (shown by noncumulus rocks) between Mg′ and Al2O3, the relatively high Mg′ values of the flows, and the alkaline nature of the rocks distinguish them from most flood basalts and relate them to rift basalts. Low Al2O3 concentrations at the highest Mg′ values may be related to genesis in a garnet-rich mantle source under high pressures. These continental alkali basalts provide evidence that this portion of Avalonian terrane experienced tension during the Cambrian.
Carboniferous volcanic rocks of the Magdalen Islands, Gulf of St. Lawrence
Authors: Barr Sandra M. , Brisebois Daniel , Macdonald Alan S.
Published: April 2011

Volcanic rocks of Mississippian age occur on the Magdalen Islands as cap rocks and within collapse breccias above salt diapirs that have formed the islands. They consist of coarse volcaniclastic deposits and basaltic flows, intruded by minor mafic dykes and plugs. Petrologic studies of the basaltic rocks show that they are extensively altered. Original plagioclase, clinopyroxene, olivine, and interstitial glass are partially to entirely replaced by mixtures of chlorite, sericite, smectite, sphene, carbonate, epidote, albite, potassium feldspar, and iron oxides, and the samples display a relatively wide range in chemical compositions. Especially mobile were K, Na, and Ca, and most samples are classified as potash spilites (poenites). Using standard discriminant diagrams for mafic igneous rocks, it can be seen that the basalts appear to range from continental tholeiitic to continental alkalic. However, relict clinopyroxene compositions and the presence of kaersutitic amphibole and titaniferous biotite in some samples imply that the suite may originally have been more alkalic than tholeiitic.
Interpreting paleoclimate from l8O and 2H in plant cellulose: comparison with evidence from fossil insects and relict permafrost in southwestern Ontario
Authors: Edwards T. W. D. , Aravena R. O. , Fritz P. , Morgan A. V.
Published: April 2011

The oxygen-isotope content of terrestrial plant cellulose is related to that of the source waters by a two-step process involving evapotranspirative leaf-water enrichment and equilibrium isotopic exchange between leaf water and atmospheric carbon dioxide. A combination of two models that describe these steps yields consistent agreement between measured and predicted climatic and isotopic data. Humidity is the dominant influence on variations in the cellulose 18O enrichment relative to the source water. A good first-order approximation of the average daytime relative humidity during the growth season at a site can be based on the linear correlation that exists between humidity and cellulose enrichment, without explicit consideration of factors such as temperature, δ18O of atmospheric vapour, and leaf boundary-layer dynamics.The value of the combined model for paleoclimatic reconstruction has been tested using fossil wood from a late glacial site at Brampton, Ontario. Estimates of the past relative humidity were derived from the divergence between measured δ18O values of fossil wood cellulose and environmental water isotopic compositions inferred from the carbon-bound deuterium contents of the cellulose. Growing conditions were apparently substantially drier than those at present between about 11 500 and 8700 years BP, at a time when coniferous forests predominated in southwestern Ontario. A shift in the inferred meteoric water composition over this period suggests a gradual increase in mean annual temperature of about 2 or 3 °C, in agreement with estimates of temperature change based on paleoentomological data.
Evidence for a Neoglacial advance of the Boundary Glacier, Banff National Park, Alberta
Authors: Gardner James S. , Jones Norman K.
Published: April 2011

Direct evidence for an early Neoglacial advance in the Canadian Rocky Mountains is presented. Radiocarbon dates from buried peat and tree remains at Boundary Glacier suggest limiting dates for this advance of between 3800 and 4200 years BP. These data from Boundary Glacier are consistent with previously published dates for the onset of the Neoglacial and an early Neoglacial advance.
Use of an ablatometer to measure short-term ablation of exposed ground ice
Authors: Lewkowicz Antoni G.
Published: April 2011

An instrument (ablatometer) was developed to measure rates of ablation of exposed ground ice. When the ablatometer is mounted on a melting ice face and linked to a portable micrologger, a continuous record of short-term ablation is obtained.The ablatometer was tested on the headwall of an active ground-ice slump located in southwest Banks Island, Northwest Territories. In general, it performed satisfactorily with little or no instrument-induced melt of the ice. Data for sunny days showed a strong diurnal rhythm of ground-ice ablation and considerable microscale spatial variability. Rates of ablation and their spatial variation were lower on cloudy days, illustrating the importance of solar insolation in inducing melt. Measurements beneath a debris cover following active-layer collapse suggest that ablation soon ceases and does not recommence until after the debris is removed by mud flow.As a result of the high degree of spatial variability in energy inputs and consequently in ablation rates, results from a single ablatometer may not be representative. If two or more instruments are mounted concurrently on exposed ice, an average value of the energy used in ablation can be determined. This value can then be compared with measurements of energy fluxes such as net radiation.
Post-Aphebian uplift deduced from remanent magnetization, Yellowknife area of Slave Province
Authors: Schwarz Erik J. , Buchan Kenneth L. , Cazavant Alain
Published: April 2011

Remanent magnetization in five Indin, three Dogrib, two Archean, and one Mackenzie dyke contact zone(s) from the Yellowknife area of the Canadian Precambrian Shield has been studied in order to establish the ambient temperature of the host rock and the depth of burial of the present erosion surface at the time of intrusion. A positive baked-contact test for an Aphebian Indin dyke demonstrates the primary nature of the dyke magnetization. From this contact, eight individual specimen determinations of the ambient host-rock temperature at the time of intrusion yield an average of 211 °C, with a standard deviation of 18 °C and probable error of ± 36 °C. Assuming a paleogeothermal gradient of 44 °C/km (± 30%) the estimated depth of burial of the present erosion surface is [Formula: see text]. None of the remaining contacts yield estimates of the depth of burial. However, the results from the three Dogrib contacts illustrate complications such as chemical overprinting that must be considered when analysis is made of magnetization in igneous contact zones. Thus, only one spot reading of the depth of burial of the area has been obtained. Correlation of the Indin result with a result from the Matheson area of Ontario and with stratigraphic indicators is uncertain because of large intervening distances and the occurrence of younger structural zones.
REE mobility due to alteration of Indian Ocean basalt
Authors: Seifert Karl E. , Cole Melanie R. W. , Brunotte Dale A.
Published: April 2011

Indian Ocean basalts from DSDP site 249 on the Mozambique Ridge exhibit a progressive up-hole increase in alteration and Fe2O3/FeO and decrease in MgO and density over the approximately 3.5 m of recovered core. Abrupt increases in H2O+ and K2O and a decrease in CaO relative to lower basalt samples occur in the uppermost sample. These up-hole changes are accompanied by increasing REE and LREE/HREE and the development of a pronounced negative Ce anomaly. A rough estimate of the magnitude of chemical change is obtained by holding our most immobile element (Lu) constant.
Geochemical indicators in lake sediment of upland erosion caused by Indian and European farming, Awenda Provincial Park, Ontario
Authors: Burden Elliott T. , Norris Geoffrey , McAndrews John H.
Published: April 2011

Neutron-activation analysis, loss on ignition (LOI), and X-ray diffraction of eight cores collected in Second and Gignac lakes are correlated with historic and palynologic records to identify elements linked to erosion from deforestation and farming.Forest disturbance and farming are identified in cores of organic detritus sediment (gyttja) by decreased LOI and increased Na, Mg, Ba, Al, Ti, and Dy. LOI is not suitable for identifying forest disturbances in carbonate sediments. From neutron-activation analysis of carbonate mud only Na, Al, and Dy indicate erosion.Elements linked to the quantity of organic matter in sediments include U, V, and Cl, whereas Mn and I in surface sediments presumably correspond with variations in the oxidation potential and plant productivity, respectively.Sedimentation patterns relate to basin morphology. In Gignac Lake the basin is steep sided and relatively deep. Clastic detritus entering the lake is carried over the shallow, nearshore carbonate bank into deeper water. In Second Lake the basin is shallow and gently sloping. Minerals eroded from onshore are more equally distributed in this basin. In Second Lake the most rapid sedimentation is nearshore where submerged aquatic macrophytes produce and trap carbonate mud. In Gignac Lake the top of the shallow carbonate bank has few aquatic macrophytes; lime mud formed on the bank is washed into deep water offshore, where it dissolves.
A U–Pb age for mineralized Nipissing diabase, Gowganda, Ontario
Authors: Corfu F. , Andrews A. J.
Published: April 2011

Concordant baddeleyite and rutile analyses from mineralized Nipissing diabase at Gowganda's Castle mine yield a U–Pb age of [Formula: see text]. Baddeleyite is a primary phase of the diabase; therefore the age dates the magmatic emplacement. The genesis of rutile is less certain: rutile could have formed during an episode of alteration, veining, and Ag mineralization, in which case the U–Pb age would also date the secondary event and demonstrate that Ag mineralization was related to the Nipissing magmatism. However, a primary magmatic origin of the rutile cannot be completely excluded for now; thus the U–Pb age may not constrain the time of Ag mineralization. Further research is needed to clarify this point.
New and revised acritarch taxa from the Upper Devonian (Frasnian) of Alberta, Canada
Authors: Turner Robert E.
Published: April 2011

Topotypes of Multiplicisphaeridium? sprucegrovensis Staplin have been obtained using modem processing techniques. Examination of these with sophisticated optical and electron microscopes has revealed important morphologic features not recorded in the original description. These data, combined with a restudy of Staplin's holotype and paratype, require a new combination, Craterisphaeridium sprucegrovense. Some specimens attributed in the literature to this taxon may belong to Puteoscortum williereae Martin. The differences that separate these taxa are emphasized. A third taxon, Pertusisphaeridium dispar gen. et sp. nov., is described for the first time. It is similar to C. sprucegrovense comb. nov. in gross morphology but is distinctly different in detail. A new type of excystment structure, the pelecinate median split, is described from this form and is shown to occur also in C. sprucegrovense.
Geochemical constraints on the differentiation processes that were active in the Sept Iles complex
Authors: Higgins Michael D. , Doig R.
Published: April 2011

Major- and trace-element abundances in the major units (gabbro, anorthosite, monzonite, syenite, and granite) of the unmetamorphosed Sept Iles complex have been evaluated to determine if these rocks can be related by simple magmatic processes or if it is necessary to invoke separately derived magmas. Major-element mass-balance and trace-element distribution calculations indicate that the diorite and quartz syenite were produced by fractional crystallization of plagioclase and augite, together with minor hypersthene and ilmenite, from a parental gabbroic magma. The Sr depletion of the granite, as compared with the quartz syenite, cannot be developed readily by partial melting and is better explained by fractional crystallization models. Major-element mass-balance solutions indicate that the granite was formed by removal of alkali feldspar, plagioclase, amphibole, and ilmenite from a quartz syenitic magma. Depletion of REE in the granite was probably the result of amphibole or REE-rich accessory mineral fractionation. It is unlikely that an unrelated, independently generated granitic magma could have a composition so related to the remainder of the complex. Therefore, fractional crystallization of a parental gabbroic magma is the dominant process that controlled the diversity of magma in the complex.
Assemblages de chitinozoaires dans l'Ordovicien inférieur de l'est du Canada
Authors: Achab Aicha
Published: April 2011

From a description of middle Arenig Chitinozoa from the Levis Formation (Zone C) and the Cow Head Group, a succession of the main Lower Ordovician chitinozoan assemblages is proposed.This succession is compared with the main assemblages described in the literature. This comparison allows recognition of taxa with potential stratigraphie value.
Penecontemporaneous sandstone dykes, Nonacho Basin (early Proterozoic, Northwest Territories): horizontal injection in vertical, tabular fissures
Authors: Aspler Lawrence B. , Donaldson J. A.
Published: April 2011

Sandstone dykes in Proterozoic sedimentary rocks of Nonacho Basin cut only the fine-grained portions of cyclic fluvial, pond, and lacustrine deposits but occur repetitively through hundreds of metres of section. Such restriction to specific beds, in conjunction with erosional truncations of the dykes and association with sand volcanoes, indicates that the dykes are penecontemporaneous. Minimal compaction-related deformation, sharp dyke walls, and mud chips within dykes suggest that the fine-grained host rocks were cohesive before dyke emplacement. In sections parallel to bedding, the dykes are polygonal; normal to bedding, dyke configurations range from tabular to branching to fully developed reticulate networks. The dykes are generally massive, but grain size locally increases towards dyke centers. In contrast to most dykes described in the literature, internal stratification is generally at high angles to dyke walls and at low angles to sill walls.Of the hypotheses considered for dyke emplacement (sedimentary infill, hydroplastic squeezing, fluid injection, and foundering of the flanks of sand volcanoes), fluid injection is favoured as the most likely mechanism. Concurrent mudstone Assuring, sand liquefaction, and injection are attributed to earthquake shocks. Vertical fissures were filled with sand that was injected horizontally, a phenomenon not commonly reported. Widespread stratigraphic distribution of the dykes and an abundance of other soft-sediment deformation structures attest to numerous tectonic disturbances during sedimentation in Nonacho Basin.
The Thallograptus and Diplospirograptus from the Silurian Eramosa Member in Hamilton (Ontario, Canada)
Authors: Hewitt R. A. , Birker I.
Published: April 2011

The holotypes of Buthotrephis grantii Dawson and Inocaulis vegetabilis Gurley are adjacent parts of a single 0.24 m wide colony from the Eramosa Member of the Lockport Dolomite in Hamilton, Ontario. The currently accepted name of Inocaulis vegetabilis, Thallograptus vegetabilis, is a junior objective syonym of T. grantii. Diplospirograptus dubius (Spencer) was found in the same horizon and facies as T. grantii. They are interpreted as a possible algal forest situated above an offshore deoxygenated sediment. The alternative graptolite or plant affinities of these two genera remain in doubt.
Structure and function of a conduit aquifer
Authors: Smart C. C. , Ford D. C.
Published: April 2011

The hydrological function of a karst aquifer is strongly controlled by its physical structure. Observations of physical hydrology and water chemistry along with artificial tracing allow aquifer behaviour to be identified so that hypothetical aquifer structures can be envisaged. Such structures can be evaluated in terms of the geology and geomorphology of the area in question and explained in terms of the geomorphological evolution of the aquifer. A study of the Castleguard Meadows karst aquifer (Rocky Mountains, Alberta) is used to demonstrate this. Four karst springs (one perennial, the remainder intermittent) in one group are considered to be the outlets to a number of conduits. The oldest and largest of these is possibly choked by sediment and acts as a reservoir rather than a conduit, while others convey overflow floods from the upper Saskatchewan Glacier. The aquifer is of great antiquity but has been disrupted by glaciation. The aquifer model developed is a simple hypothesis but provides a valuable research tool suitable for both simulation modelling and the design of further field experiments.
U–Pb zircon ages in supracrustal and plutonic rocks; North Spirit Lake area, Northwestern Ontario
Authors: Corfu F. , Wood J.
Published: April 2011

The North Spirit Lake greenstone belt in the Sachigo Subprovince of the Superior Province comprises parts of three sequences of volcanic and sedimentary rocks; the main (youngest) is separated from the older sequences by an unconformity to disconformity. The belt is bounded by large granitoid batholiths and was metamorphosed under greenschist to, locally, hornblende–cordierite facies. U–Pb zircon dating was performed on volcanic, sedimentary, and plutonic rocks in order to establish an absolute chronology for the evolution of the area.A tuff breccia in the lowermost supracrustal sequence is dated at 3023 ± 2 Ma. Zircons from a tuff in the middle sequence show complex U–Pb relationships; although they do not allow a precise age determination, the data suggest that the tuff formed sometime between 2950 and 2800 Ma ago. Zircons from a quartz arenite, also in the middle sequence, yield a simple data pattern and define an age of [Formula: see text], suggesting derivation of the sediment from a uniform source of this age. A zircon analysis from a tonalitic clast in a conglomerate at the base of the upper sequence yields a minimum age of 2975 Ma. The clast may have had the same origin as the zircons in the quartz arenite. Another tonalitic clast from the same conglomerate yields a slightly older age of 3001 ± 3 Ma. No remnant of these tonalites can be recognized in the field, suggesting that they have been largely removed during subsequent erosional processes.Two subvolcanic intrusions from the upper sequence yield zircon ages of 2743 ± 2 and 2731 ± 2 Ma, respectively. A crystal tuff, also in the upper sequence, contains two generations of zircons: newly formed magmatic zircons, which date the extrusion of the tuff at 2735 ± 10 Ma, and older grains with a minimum age of 2862 Ma, which represent inherited zircons. This tuff was thus generated at least in part by anatectic melting of >2862 Ma crust.A quartz diorite from MacDowell Lake in the adjacent Berens River Subprovince yields an age of 2744 ± 2 Ma. A mafic inclusion in the quartz diorite contains amoeboidal, strongly fractured zircons, which point to an intercept age of about 2727 Ma. This age could either reflect a metamorphic event or represent a geologically meaningless mixed age.
The Jurassic ammonite Pseudolioceras (Tugurites) of the Bering Province
Authors: Sey I. I. , Kalacheva E. D. , Westermann G. E. G.
Published: April 2011

Two species groups can be distinguished in the evolution of Pseudolioceras s.l. The first ranges through most of the Toarcian (and? earliest Aalenian) and makes up the circum-Boreal Pseudolioceras s.s. The second extends through the Aalenian and earliest Bajocian of the Bering Province and constitutes the subgenus Tugurites, of considerable chronostratigraphic importance.
The Cretaceous–Tertiary boundary In the central Alberta Foothills. I: Stratigraphy
Authors: Jerzykiewicz T. , Sweet A. R.
Published: April 2011

The Cretaceous–Tertiary boundary in the Rocky Mountain Foothills occurs within a continental sequence carrying economic coal deposits and known as the Coalspur Formation. This formation occurs between the fluvial Brazeau (below) and Paskapoo formations. The exact position of the boundary is located at the base of the lowest coal (Mynheer) within the Coalspur Formation. The initiation of coal deposition in the Coalspur Formation is not a unique event, as it is consistent with the cyclic pattern established within the underlying Brazeau Formation. However, the magnitude and lateral continuity of coal zone development far exceed those found in the underlying formation.The classic shift from a diverse, late Maastrichtian flora (within which angiosperm and especially aquiloid pollen are prominent) to a low-diversity, Early Paleocene flora dominated by gymnosperm pollen and miospores is documented. Deviations from most previously recognized floral events at the Cretaceous–Tertiary boundary include (1) san angiosperm pollen peak immediately above the determined boundary position (formed by two dominant species, Syncolporites minimus and Triporopollenites plektosus) and (2) the extension of the range of species of aquiloid pollen into the Paleocene.
Ziegler's Blisters in Pentameroides from a Lower Silurian fossil locality in the northeastern part of the Mascarene–Nerepis Belt, southern New Brunswick
Authors: Boucot A. J. , McCutcheon S. R.
Published: April 2011

The teratological condition known as Ziegler's Blisters is reported for the first time in the pentameroid brachiopod Pentameroides. This reinforces the conclusion that Pentameroides was descended from the genus Pentamerus, which also has the same condition, i.e., Ziegler's Blisters. This is also the first time that a paleoteratological condition has provided evidence to support a previously deduced evolutionary conclusion based on skeletal morphology alone. The relatively shallow, rough water conditions deduced from paleoecologic consideration of the entire fauna accompanying the teratological specimens is supported by sedimentologic data. The fossil locality is from near the base of the Silurian section in the northeastern part of the Mascarene–Nerepis Belt.
Distribution of biogenic silica in the surficial sediments of Lake Michigan
Authors: Conley Daniel J. , Schelske Claire L. , Dempsey Brian G. , Campbell Charles D. , Newberry Teresa L.
Published: April 2011

The spatial distribution of biogenic silica (BSi) in the surficial sediments of Lake Michigan is described from Shipek grab samples collected in 1975 and gravity cores obtained in 1983. Significantly smaller surficial BSi concentrations in the 1975 samples were attributed primarily to the inability of a Shipek grab to collect intact surficial sediment samples. Lower concentrations o.f BSi were found in nondepositional and transitional areas of sediment accumulation than in depositional basins. Therefore, BSi accumulation is restricted primarily to the 40% of the lake bottom where sediments are presently accumulating. High concentrations found in Green Bay surficial sediments are related to high productivity in the bay coupled with inputs of new silica from the Fox River. In the open lake, BSi concentrations of surficial sediments in depositional basins appeared to vary inversely with sedimentation rate in that lower BSi concentrations were found in areas with higher sedimentation rates.
A new technique for sampling water and gas from deep drill holes
Authors: Nurmi Pekka A. , Kukkonen Ilmo T.
Published: April 2011

A new technique for sampling water and gas from deep (500–1500 m) drill holes is described. The principle of the technique is to raise a continuous column of water inside a thin polyamide tube with a back-pressure valve at the lower end and with shutoff valves every 50 m. The equipment is easily assembled from standard parts. Sampling can be performed by three people without mechanical apparatus. Descent to 1000 m takes 2 hours and retrieval 1 hour. The method makes it possible to obtain a practically undisturbed continuous water profile from a drill hole. Dissolved gases remaining inside the tube can be sampled at the surface. To demonstrate the efficiency of the technique, selected results from the deepest drill hole in Finland, having a vertical depth of 1100 m, are presented.
Till variability and compositional stratification: examples from the Port Huron lobe
Authors: Broster Bruce E.
Published: April 2011

Compositional variability provides important clues to the glacigenic mechanisms of entrainment and transportation of debris and deposition of basal tills. This paper examines contrasting homogenization and stratification of textural and geochemical composition for two late Wisconsinan till units, exposed in a near-vertical section at Port Albert, Ontario. Q-mode cluster and multivariate discriminant analysis are used to delineate compositional layers, which occur in both units, although in the upper unit the distinction is less noticeable because of compositional homogeneity. It is inferred that compositional stratification is inherent in the entrainment process, whereas englacial thrusting and shearing tend to homogenize the glacial load. It is suggested that recognition of the degree of homogenization or the occurrence of stratification is essential for the application of analytical results in the study of till units.
Caractérisation du magmatisme Protérozoïque supérieur en Afrique de l'ouest et implications géodynamiques : des rifts intracratoniques au Panafricain?
Authors: Dupont P. L. , Lapierre H. , Gravelle M. , Bertrand J. M.
Published: April 2011

The main petrological, mineralogical, and geochemical features of the metavolcanites belonging to the Late Proterozoic tectono-sedimentary units of southern Mauritanides (Termessé and Niokolo Koba – Koulountou) and western Hoggar, Algeria (Timesselarsine), permit a reconstruction of the geodynamic environment that controlled the evolution of the Pan-African ranges of western Africa. Flows and pyroclastic beds metamorphosed under greenschist-facies conditions are interbedded within detritic and carbonate platform sediments, suggesting an unstable environment in the vicinity of a continental margin.The association of oceanic tholeiites slightly enriched in LREE and basalts more enriched in TiO2, Zr, Nb, and LREE displaying alkalic affinities suggests intracontinental rifting succeeded by expansion. The lack of ultrabasic – basic complexes (oceanic paleosutures) in southern Mauritanides and their occurrence in the Hoggar suggest that the opening was bigger in the north than in the south.The later calc-alkalic sequences of the Niokolo Koba – Koulountou units are tectonically associated with the Termessé unit. In the Timesselarsine unit, calc-alkalic acid rocks coexist with the basic lavas previously mentioned. Thus, the closure of the rift related to a continental collision appears to be later in southern Mauritanides than in the Hoggar.