bluuebunny/crossref_metadata_2025 huggingface dataset:
Paleomagnetic dating of late glacial and postglacial sediments in Lake Superior
Authors: Mothersill John S.
Published: April 2011

The oldest unit of the late Quaternary sedimentary sequence of Lake Superior consists of glacial till that was deposited about 9900 years BP during the last glacial readvance into the Lake Superior basin. The till deposits are unconformably overlain by a thin sequence of bedded sands and silts, which are overlain by a thick sequence of varved sediments (> 10 m in thickness), which in turn are overlain by postglacial silty clays.Unfortunately, 14C has not been found to be a useful tool in dating the late glacial and postglacial sediments of Lake Superior. However, paleodeclination and paleoinclination logs provide a useful method of correlating and indirectly dating cores taken of the late glacial and postglacial sediments. It is concluded from paleomagnetic dating that rhythmic sedimentation ceased before 9200 years BP in the southeastern lake proper and at about 8700 years BP in the southeastern bay areas. However, rhythmic sedimentation continued until about 8200 years BP in the northern part of Lake Superior and until about 8000 years BP in the Nipigon Bay area.
Multigeneration pitchblende from the Midwest uranium – nickel deposit, northern Saskatchewan
Authors: Powers Laura J. , Stauffer Mel R.
Published: April 2011

Four generations of pitchblende and pitchblende alteration products have been identified in the ore-mineral assemblage of the Midwest deposit. Each generation is texturally and compositionally distinctive. The formation of each generation appears to have been preceded by an episode of fracturing and brecciation, indicating extensive reworking of the deposit with time. Microprobe analysis of each generation shows decreasing Pb and increasing Si, Ca, Al, and As with successive reworking events.The earliest pitchblende noted is botryoidal and contains more Pb than subsequent generations. The botryoids were fractured and altered in an episode of brecciation that was accompanied or followed by the introduction of fluids. Second-generation massive pitchblende and pitchblende alteration products (including coffinite and uranium arsenate) enclose altered fragments of first-generation pitchblende. Of the second-generation materials, this massive pitchblende contains slightly lower amounts of Pb than first-generation botryoidal pitchblende, and the alteration products of pitchblende contain substantially less Pb. Coffinite and some As-rich pitchblende contain water. A second episode of fracturing and partial dissolution of the earlier assemblages preceded precipitation of third-generation colloform pitchblende, which contains significantly less Pb than do previous generations. The fourth and youngest episode of uranium deposition is represented by disseminated pitchblende and coffinite and by pitchblende crust and veinlets. These last phases contain the least Pb and are enriched in many minor elements. All generations are accompanied by a variety of Co-bearing Ni minerals and by illite or sericite. Other important gangue minerals are quartz, hematite, siderite, calcite, and goethite.
Relationship of hydrothermal alteration to structure and stratigraphy at the Coniaurum gold mine, northern Ontario
Authors: Piroshco Darwin W. , Hodgson C. Jay
Published: April 2011

The gold mineralized zones of the Coniaurum mine, Porcupine camp, northeastern Ontario, are on the eastern end of the northeast-trending Hollinger–Mclntyre ore system. The ore zones are quartz–ankerite (plus accessories) veins and vein systems and associated pyritic wall rock, hosted by a sequence of mafic volcanic rocks and discordant quartz–feldspar porphyry stocks of Archean age.A least altered facies and three alteration facies can be distinguished within the mafic volcanic rocks: a chlorite facies, an ankerite facies, and a vein envelope facies. The chlorite facies is widespread, overprints the least altered facies (i.e., chlorite replaces actinolite), and hosts barren and locally mineralized quartz veins bordered by vein envelope facies alteration. The ankerite facies is coextensive with subparallel shear zones, which crosscut me axial trace of the Coniaurum anticline, and hosts most of the mineralized vein systems. Addition mineralization occurs within graphitic sediments in the crest area of the Coniaurum anticline.On the basis of the above relationships, the shear zones, hydrothermal alteration, and mineralization are interpreted to be late (i.e., syn- to post-development of the Coniaurum anticline).The mineral assemblages of the chlorite and ankerite alteration facies are interpreted as resulting from lateral gradients in [Formula: see text]. Replacement textures between minerals at the alteration facies boundaries indicate the hydrothermal system first grew outwards but later collapsed inwards and the vein envelope facies is superimposed on the more widespread ankerite and chlorite facies.
Geological setting of gold, western Wabigoon Subprovince, Canadian Shield: exploration targets in mixed volcanic successions
Authors: Melling David R. , Blackburn Charles E. , Watkinson David H. , Parker Jack R.
Published: April 2011

The Archean volcanic rocks in the Cameron–Rowan lakes area may be divided into three distinct successions based on field mapping, petrographic studies, and lithogeochemical characteristics. The lowermost Rowan Lake Volcanics are tholeiitic pillowed basalts. These rocks are unconformably overlain by the Cameron Lake Volcanics, a mixed succession of tholeiitic massive and pillowed basalts and intermediate to felsic volcaniclastic rocks. The Brooks Lake Volcanics consist of tholeiitic basalts and represent the youngest volcanic rocks at the top of the preserved succession.Most of the gold concentrations in the Cameron–Rowan lakes area are confined to the mixed Cameron Lake Volcanics. The majority of these, including the Cameron Lake deposit, occur within shear zones near lithologic contacts. In the Eagle–Wabigoon and Manitou lakes areas there are similar stratigraphic subdivisions of the supracrustal rocks and many of the gold concentrations also occur in deformation zones within the mixed volcanic successions. The contrasting competencies among the basalts, the intermediate to felsic volcaniclastic rocks, and the intrusive rocks, which are characteristic of the mixed volcanic successions, localized stress during deformation, forming shear zones into which gold-bearing fluids gained access. The potential for successfully delineating economic gold concentrations appears greatest in the mixed volcanic successions within these areas and elsewhere in the western Wabigoon Subprovince of the Canadian Shield.
Uranium in groundwaters of southeastern Manitoba, Canada
Authors: Betcher R. N. , Gascoyne M. , Brown D.
Published: April 2011

Anomalously high levels of naturally derived uranium have been found in groundwater samples from wells completed in overburden and bedrock aquifers in southeastern Manitoba. Uranium analyses were carried out on groundwater samples collected from 287 individual wells in a 15 500 km2 area. The mean U concentration in all samples was 58.3 μg/L; the maximum value was 2020 μg/L. Uranium concentrations were highest in samples from Precambrian rock aquifers, averaging 115.6 μg/L, and were lowest in samples from Paleozoic sedimentary rock aquifers, averaging 3.5 μg/L.Uranium concentrations up to 250 μg/L were found in groundwaters in or associated with Lake Agassiz clay deposits. These high concentrations are thought to result principally from release of U from the organic component of the clays, either by oxidation or desorption. Leakage of uraniferous groundwater from the clays appears to provide a significant source of U to underlying sand and gravel aquifers and to the Precambrian bedrock aquifer. Uranium within the bedrock is also being released to solution by oxidation of uraniferous hematite found as mineral coatings and fracture fillings in highly weathered zones. Uranium solubility in many Precambrian bedrock groundwaters is increased by recharge of these aquifers by ground waters from overburden materials that contain high [Formula: see text] concentrations.
Variations d'épaisseur du Cambrien moyen en Meseta marocaine occidentale: signification géodynamique des données de surface et de subsurface
Authors: Bernardin Christine , Cornée Jean-Jacques , Corsini Michel , Mayol Stéphane , Muller Jacques , Tayebi Mohamed
Published: April 2011

The western part of the Moroccan Meseta contains thick Middle Cambrian terrigenous deposits, in places 7000 m thick. Field data and geophysical investigations indicate subsident grabens controlled by major N30°E and N60°E fault zones on the northwestern part of the African shield. These grabens correspond to the late evolution of an intracontinental rift that originated during Late Precambrian and Early Cambrian time and can be considered evidence of the opening of the Iapetus paleo-ocean in Morocco.
Fire Lake depression: a glacially eroded feature in southwestern Saskatchewan, Canada
Authors: Christiansen E. A. , Sauer E. K.
Published: April 2011

Fire Lake depression, which is 9 km long, 5 km wide, and about 100 m deep, was formed by surface removal of about 40 m of drift, mainly till, and 60 m of Cretaceous sands, silts, and clays. The depression, which was formed during the last glaciation, was partly filled with hummocky glaciolacustrine sands and silts. The bedrock beneath the depression is slickensided, folded, brecciated, softened, and gouged, typical of structures formed by shear.The physical dimensions, stratigraphy, structure, and age (last glaciation) indicate that the Fire Lake depression was formed by glacial erosion. The folding, faulting, brecciation, gouge, and softening of the bedrock beneath the depression are indicative of shear and suggest glacial thrusting. The process of glacial thrusting was not verified, however, because the sediments excavated from the depression were not found. The fact that the base of the depression corresponds to the uppermost, most clayey bed (least shear resistance) suggests that the depression was formed during one episode of glacial erosion.
Upper Ordovician conodonts, brachiopods, and chronostratigraphy of the Whittaker Formation, southwestern District of Mackenzie, N.W.T., Canada
Authors: Mitchell Charles E. , Sweet Walter C.
Published: April 2011

Ten samples from a 160 m section through the lower Whittaker Formation yielded Red River Province conodonts as well as a shelly macrofossil assemblage representing the "Arctic Ordovician fauna." Both the microfossils and macrofossils have strong affinities with taxa represented in strata of Cincinnatian age in the western Midcontinent Province of North America.Conodont-based graphic correlation of section W-1 with a Composite Standard Section developed for midcontinental United States indicates that the lower Whittaker Formation on the east flank of the Redstone Arch represents nearly the entire Cincinnatian Series. Trilobites of the Ceraurus mackenziensis Zone occur in strata correlative with the upper Edenian and those of the Whittakerites planatus Zone first appear at or just below the projected base of the Maysvillian Stage. The age of the Ceraurinella necra Zone is still uncertain but is likely to be early Edenian.Thaerodonta recedens (Sardeson) and other elements of the Bighornia – Thaerodonta fauna also debut in uppermost Edenian or lowermost Maysvillian strata. The morphology of Sowerbyella redstonensis n.sp. and Thaerodonta recedens from the lower Whittaker Formation indicates that the common ancestor of early Thaerodonta species may have arisen during latest Edenian time. The first appearance of Thaerodonta may constitute a useful biostratigraphic datum throughout the Red River Province. The strongly Thaerodonta-like species, Sowerbyella redstonensis n.sp., is described from silicified material of mid-Edenian age.
Stratigraphy and sedimentology of the Hamill Group in the northern Selkirk Mountains, British Columbia: evidence for latest Proterozoic – Early Cambrian extensional tectonism
Authors: Devlin William J.
Published: April 2011

Three informal stratigraphic divisions are recognized in the uppermost Proterozoic – Lower Cambrian Hamill Group in the northern Selkirk Mountains of British Columbia. These informal divisions include a lower sandstone unit, a greenstone–graded-sandstone unit, and an upper sandstone unit. Both the lower and upper sandstone units display sedimentary characteristics that are uniform along strike and indicate a shallow-marine environment of deposition. As is typical of other exposures of the Hamil Group in southeastern British Columbia, the lower sandstone unit is coarser grained and more poorly sorted than the mature quartz arenites of the upper sandstone unit.The greenstone–graded-sandstone unit is a complex assemblage of mafic metavolcanic rocks and associated sandstone facies. This unit is highly variable along strike but essentially consists of a thick succession of subaqueous extrusive rocks overlain by a variety of sediment gravity-flow deposits. These latter deposits include resedimented conglomerates, debris-flow deposits, and trubidites (deposited from both high- and low-density turbidity currents). Stratigraphic sections of this unit are described in detail from three different localities and are examined in terms of their transport and depositional mechanisms.The stratigraphic succession of the Hamill Group indicates that deposition of the shallow-marine sands of the lower sandstone unit was abruptly interrupted by a period of volcanism, the creation of a paleoslope, and the deposition of a large volume of sediment gravity-flow deposits of the greenstone–graded-sandstone unit. These relations are attributed to an episode of syndepositional normal faulting. The inferred fault(s) could have served as the conduit for the extrusion of the volcanics. Offset along the fault(s), the tilting of fault blocks, and the consequent formation of an unstable slope adjacent to a fault scarp created an environment favorable for deposition of the sediment gravity flows. In general, deposition of proximal, base-of-slope deposits was followed by an aggradational basin-fill phase of sedimentation. With the waning of tectonic activity and the filling of the fault-bounded basin, depositon of shallow-marine sands resumed (the upper sandstone unit). The stratigraphic relations of the Hamill Group in the northern Selkirk Mountains are considered direct evidence for an episode of latest Proterozoic – Early Cambrian extensional tectonism. The evidence for an episode of rift-related tectonism in the northern Selkirk Mountains supports inferences concerning the timing of this event as derived from tectonic subsidence analyses of post-rift strata of the Cordilleran miogeocline.
Late Devonian lamprophyric dykes in the Meguma Zone of Nova Scotia
Authors: Kempster R. M. F. , Clarke D. B. , Reynolds P. H. , Chatterjee A. K.
Published: April 2011

Hornblende-rich lamprophyric dykes from southeastern Nova Scotia are contemporaneous with the large peraluminous granitic batholiths (ca. 370 Ma) of the Meguma Zone and may be closely associated with their origin.
Geochemistry and U–Pb zircon age of comenditic metafelsites of the Tibbit Hill Formation, Quebec Appalachians
Authors: Kumarapeli P. Stephen , Dunning Greg R. , Pintson Hillar , Shaver Jim
Published: April 2011

Metafelsites in Waterloo area, Quebec, represent the only known silicic volcanic rocks in the predominantly basaltic Tibbit Hill Formation. Low-grade metamorphism accompanied by hydration and albitization has converted the felsic volcanic rocks mainly to muscovite–quartz–albite schists. The volcanic parent of these metafelsites was formed partly as lava flows and partly as tuffs. The principal compositional type was a comendite. A component of intermediate rocks is also present but its extent is undetermined and probably minor. U–Pb zircon studies of the metafelsites have yielded a reliable age of [Formula: see text]. This Early Cambrian age is probably representative of the age of the Tibbit Hill Formation as a whole.The Tibbit Hill Formation accumulated at one of the clearest examples of a RRR (rift–rift–rift) triple junction–the Sutton Mountains triple junction–of the continental rift system formed as a prelude to the opening of the Iapetus Ocean. Its volcanic rocks are products of the youngest major episode of rift-related volcanism known from the continental margin of Laurentia. The volcanic event may have occurred as a harbinger of the onset of sea-floor spreading at the Sutton Mountains triple junction.
Subaqueous phreatomagmatic explosion breccias at Buttercup Hill, Noranda, Quebec
Authors: Gibson H. L. , Watkinson D. H. , Comba C. D. A.
Published: April 2011

Irregular, branching, white-fragment breccia dikes are restricted to the uppermost flows of the Amulet formation, where they occur within or are parallel to synvolcanic faults. At Buttercup Hill, the breccia dikes bifurcate upward and are continuous with a localized deposit of identical, conformable breccia within the lowermost andesitic flows of the Millenbach andesite formation. The dikes are shallow, poorly sorted intrusive breccias and like the overlying, conformable breccia deposit are characterized by white, angular fragments of variably silicified andesite derived from the immediately underlying Amulet formation and, to a lesser extent, from the Millenbach andesite formation. The fragments show a complete range in size from 0.5 m to < 1 cm and occur within a finer matrix that includes fine ash, broken feldspar crystals, and chloritized sideromelane shards. Sideromelane shards are foreign, juvenile fragments derived from underlying andesitic magma emplaced as dikes during the onset of volcanism.Breccias at Buttercup Hill were emplaced during successive, shallow, phreatomagmatic eruptions where rising andesitic magma contacted an external fluid. The coarse, conformable breccia at Buttercup Hill is similar to "explosion breccias," which constitute the basal deposits of subaerial maar volcanoes, which form during initial crater development. Buttercup Hill breccias and numerous other breccia dikes record a period of widespread hydrovolcanic eruption prior to and during the onset of andesitic magma resurgence that eventually infilled the Noranda cauldron.
Deposition and alteration of volcaniclastic strata in two large, early Proterozoic iron-formations in Canada
Authors: Hassler Scott W. , Simonson Bruce M.
Published: April 2011

The Gunflint Iron-formation of western Ontario and the Sokoman Iron-formation of the Labrador–Quebec geosyncline both contain interbeds of coarse-grained volcaniclastic detritus. Volcaniclastic beds in the Gunflint are typically less than a metre thick and display normal grading and other physical structures typical of high- and low-density turbidites. Similar volcaniclastic beds are present in the Sokoman, as well as thicker accumulations with structures indicative of deposition from high-density turbidity currents. The volcaniclastic detritus in both iron-formations consists largely of well-sorted vitric ash and lapilli with accessory holocrystalline grains and solitary feldspar crystals. Internal textures of the vitric grains, plus the presence of armored lapilli in the Gunflint, suggest they are products of hydroclastic eruptions. However the clasts in most beds are heterogeneous and well-rounded, indicating they are sedimentary rather than eruptive deposits. Quench textures, coalesced vesicles, and diabasic textures indicate that the volcaniclastics were originally basaltic in composition, but the rocks have been pervasively altered to iron-rich chlorite, calcite, and K-feldspar (Or98 Ab2 An0) with minor quartz and illite. In addition to being pseudomorphs after the original volcaniclastic textures within grains, these minerals also occur as interstitial and vesicle-filling cements. Fibrous rims of chlorite and poikilotopic to blocky calcite are the most abundant cement types. Cementation commenced early, inasmuch as some zones show little evidence of compaction. Patterns of cementation and alteration may indicate that geothermal gradients in such iron-formation basins were steeper than they are in the most closely comparable modern settings, namely passive margins.
A method of sampling clast-rich laminated diamictons for magnetic analyses
Authors: Coyle David A.
Published: April 2011

The sampling of nonlithified diamictons for magnetic analyses (anisotropy of magnetic susceptibility and paleomagnetic remanence) has been restricted to samples that are either massive, clay-rich sediments, or fine-grained ones with very low pebble contents. A new method was developed that produced standard-sized 2 × 2 × 2 cm cubes of sediment from a laminated, clay-poor diamicton from southern Denmark. The sampling procedure did not affect the sample or its magnetic characteristics in any observable manner.
Holocene sea-level change and delta growth: Fraser River delta, British Columbia
Authors: Williams Harry F. L. , Roberts Michael C.
Published: April 2011

The Fraser River has been building its delta into the Strait of Georgia in southwestern British Columbia for about the last 9000 years. This period encompassed a relative sea-level rise of some 13 m. This study concerns the effects of the rise in sea level on the depositional evolution of the delta.The lithostratigraphy of the delta was established by a series of drill cores. Four major lithostratigraphic units were defined: peat, organic-rich silt, interbedded silts and sands, and massive sands. These units were interpreted in terms of the delta's contemporary depositional environments, including peat bog, floodplain, and intertidal zone.Analysis of the delta's depositional architecture and chronology indicates that the delta continued to prograde during the rise in sea level. A marine transgression, accompanied by the landward migration of marine and intertidal facies, did not occur. Growth of the delta during the rise in sea level was accomplished by both vertical accretion and lateral progradation.Vertical-accretion rates during the rise in sea-level averaged 2.4 mm/year and ranged up to about 5.3 mm/year. Lateral progradation of the delta was most rapid in the early stages of growth (9000 – 8000 years ago), when the average rate was 6.5 m/year, and slowest during the period of most rapid sea-level rise, when the rate declined to less than 1 m/year. The progradation rate of 2.4 m/year calculated for the most recent period (2250–present) compares well with estimates based on bathymetric surveys.A revised sea-level curve for the Fraser Lowland region is proposed on the basis of the identification of former sea-level positions in core at the lithologic transitions from tidal-marsh to intertidal deposits. The curve contains a hitherto unknown stillstand that occurred ca 6000 years ago and shows that the mid-Holocene sea-level rise continued until about 2250 years ago.
U–Pb zircon geochronology in the southwestern Abitibi greenstone belt, Superior Province
Authors: Corfu F. , Krogh T. E. , Kwok Y. Y. , Jensen L. S.
Published: April 2011

The Abitibi Belt is the largest continuous greenstone belt in the Superior Province of the Canadian Shield. It comprises several composite komatiitic–tholeiitic–calc-alkalic and sedimentary sequences that are folded, transected by major faults, and intruded by various generations of plutonic rocks. Precise U–Pb geochronology has been carried out in the belt for the past decade to solve chronostratigraphic and metallogenetic problems. This paper presents new zircon ages and reassesses previously published ones, now refined by the addition of abraded and concordant zircon analyses.Volcanic and subvolcanic units of the Timmins area yield the following ages: 2727 ± 1.5 Ma for a tuff of the upper Deloro Formation; 2703 ± 1.5 Ma for a tuff of the upper Tisdale Formation; and 2698 ± 4 Ma for the Krist fragmental, assigned to the top of the Tisdale Formation. The age of a dunite intrusive into the upper Deloro Formation is revised at 2707 ± 3 Ma, whereas the Aquarius diorite east of Timmins yields a poorly defined age of 2705 ± 10 Ma. In the Lake Abitibi – Kirkland Lake region, the following dates were obtained: 2713 ± 2 Ma for a porphyritic unit of the Hunter Mine Group; 2714 ± 2 Ma for a rhyolite at the base of the mainly tholeiitic to komatiitic Stoughton–Roquemaure Group; 2701 ± 2 Ma for porphyritic rhyolite of the Blake River Group; 2701 ± 2 Ma for a tuff of the Skead Group; and [Formula: see text] for a pyroclastic unit at the base of the Larder Lake Group. These data are generally consistent with the earlier proposed stratigraphic subdivisions and correlations. However, there are apparent age reversals, for example between the Larder Lake and Skead groups, that could support the concept of thrusting and tectonic thickening to explain particular lithologic relationships and the considerable stratigraphic thickness of the supracrustal sequences in the Abitibi Belt.One part of the study was dedicated to the problem of gold mineralization in the Timmins area. The zircon age of 2690 ± 2 Ma for the Paymaster porphyry, a less well defined but probably identical age for the Preston porphyry, and dates of 2689 ± 1 Ma for the Pearl Lake porphyry, 2691 ± 3 Ma for the Millerton porphyry, and 2688 ± 2 Ma for the Crown porphyry show that these intrusions were formed during a well-defined, short-lived episode unrelated to volcanism; furthermore, a date of [Formula: see text] for an albitite, which predates Au mineralization, demonstrates that Au is spatially but not genetically related to the porphyries.Finally, two ages are reported for late tectonic potassic intrusions: a refined age of 2678 ± 2 Ma for the Garrison stock east of Matheson and a precise zircon (and titanite) age of 2680 ± 1 Ma for the Otto stock near Kirkland Lake.
Acadian strike-slip tectonics in the Gaspé region, Quebec Appalachians
Authors: Malo Michel , Béland Jacques
Published: April 2011

At the southern margin of the Cambro-Ordovician Humber Zone in the Quebec Appalachians, on Gaspé Peninsula, three structural units of Middle Ordovician to Middle Devonian cover rocks of the Gaspé Belt are in large part bounded by long, straight longitudinal faults. In one of these units, the Aroostook–Percé anticlinorium, several structural features, which can be ascribed to Acadian deformation, are controlled by three subparallel, dextral, strike-slip longitudinal faults: Grande Rivière, Grand Pabos, and Rivière Garin. These faults follow bands of intense deformation, contrasting with the mildly to moderately deformed intervals that separate them.Most of the structural features observed – rotated oblique folds and cleavage, subsidiary Riedel and tension faults, and offsets of markers – can be integrated in a model of strike-slip tectonics that operated in ductile–brittle conditions. A late increment of deformation in the form of conjugate cleavages and minor faults is restricted to the bands of high strain. An anticlockwise transection of the synfolding cleavage in relation to the oblique hinges may be a feature of the rotational deformation.The combined dextral strike slip that can be measured within the three major longitudinal fault zones amounts to 138 km, to which can be added 17 km of ductile movement in the intervals, for a total of 155 km.
Tremadocian (Early Ordovician) nauplius-like larvae from the Middle Arm Point Formation, Bay of Islands, western Newfoundland
Authors: Roy Kaustuv , Fåhraeus Lars E.
Published: April 2011

Nauplius-like larvae are reported from the Middle Arm Point Formation, Bay of Islands, western Newfoundland. The larval specimens are characterized by an ovoid body with three pairs of uniramous appendages and a prominent labrum. Also described is a microfossil consisting of a spherical body with (probably) three appendages protruding through an opening. The larval specimens are associated with conodonts indicative of a Tremadocian (Early Ordovician) age.
Holocene paleohydrology of central Alberta: testing the general-circulation-model climate simulations
Authors: Schweger Charles E. , Hickman Michael
Published: April 2011

Paleoecological investigations of 28 lakes and bogs provide the basis for a Holocene paleohydrological record for central Alberta. Shallow basins, empty during the early Holocene, began flooding shortly after 8000 years ago; most filled from 6500 to 4500 years ago, and none filled later than 3000 years ago. Pollen of a hypersaline indicator genus, Ruppia, was found in cores of lakes where the plant does not presently grow, indicating lower lake levels, evaporation stress, and increased salinity from 8000 to 3000 years ago. Moore Lake (54°30′N, 100°30′W) may have dropped 15 m from 9200 to 5900 years ago, and Lofty Lake (54°44′N, 112°29′W) largely dried up between 8700 and 6300 years ago. Lower water levels are suggested for several lakes by shifts in fossil diatom populations from planktonic to benthic, particularly epipelic species including pioneering taxa. These shallow, warm lakes were highly productive and sedimentary pigment levels reached maximum values between about 9000 and 4000 years ago.The paleohydrological record indicates early Holocene aridity, with the onset and development of moister conditions between 8000 and 3000 years ago, by which time modern climatic and vegetation conditions had been established. This record fits the Holocene climate predicted by the general-circulation-model simulations based on orbital perturbations.
Late Holocene aggradation in the lower Humber River valley, Toronto, Ontario
Authors: Weninger J. M. , McAndrews J. H.
Published: April 2011

Alluvial fills are common in the lower reaches of rivers along the western shore of Lake Ontario. The Humber River floodplain at Toronto is underlain by a 2.5 km long wedge of alluvium that thins upstream from Lake Ontario. Floodplain sediments were studied for their lithology, 14C age, and fossil pollen. On the levees, grey clay is overlain by oxidized silt and sand. Sediment cores from two flood ponds grade upward from gravel, sand, and silt, to silty marl, mineral peat, and clay, to heterogeneous silt and sand. Base-level (Lake Ontario) rise directly controlled aggradation between 6500 and 1800 years ago, after which time base level no longer directly controlled aggradation because levees had emerged alongside the channel and reduced the supply of sediment to the floodplain. For the past 150 years, upstream forest clearance and urbanization increased sediment input to the floodplain, broadened the levees, and filled the flood ponds.Average flood-pond aggradation rates were estimated from seven 14C dates; these rates declined from 65 cm/100 years between 6500 and 3800 years ago, to 47 cm/100 years between 3800 and 3400 years ago, to 26 cm/100 years between 3400 and 1800 years ago. These rates reflect contemporaneous lake-level rise. Between 1800 and 150 years ago, the average aggradation rate declined below the estimated rate of lake-level rise to 14 cm/100 years. Since then, the average aggradation rate has increased tenfold to 140 cm/100 years, surpassing the historic rate of lake-level rise of 23 cm/100 years. Fossil pollen from the flood ponds reflects local flood plain and regional upland vegetation during the past 4000 years.
Sedimentary processes along Flemish Pass, offshore eastern Canada: a GLORIA and high-resolution seismic reconnaissance
Authors: Jacobs Colin L.
Published: April 2011

Long-range sidescan sonar data, as well as deep-towed high-resolution seismic, 10 and 12 kHz echogram, and core data, have allowed an overview of the various sedimentary processes operating along the length of Flemish Pass. At the southern end of the pass profile data reveal that geostrophic currents are actively eroding the flanks of sediment drifts. Depositional lobes at the foot of slope gullies in the centre of Flemish Pass are characterized by elongate diapiric structures around their margins and may have triggered turbidity currents that spread across the floor of the pass. The northern margin of Flemish Pass shows evidence of (possibly historic) downslope sediment movement.
Infiltration of de-icing road salts in aquifers: the Trois-Rivières-Ouest case, Quebec, Canada
Authors: Locat Jacques , Gélinas Pierre
Published: April 2011

The results of an extensive hydrogeological investigation of the effects of de-icing road salts on Highway 55 near Trois-Rivières-Ouest indicate that a salt lens with chloride concentrations exceeding 800 mg/L exists below the highway. Maximum chloride concentration at the nearby pumping wells, not exceeding 140 mg/L, is reached only in late summer, whereas the maximum chloride infiltration follows the spring snowmelt. About 1 year's worth of road salts is retained in the unsaturated zone. The salt lens, in the upper part of the aquifer beneath the highway, has developed to a thickness of 8 m and a width of 400 m and constitutes a linear source of salts for the aquifer. The shape of this lens is distorted by the action of the pumping wells, and the lens is partly depleted by the end of the summer. Because of the particular characteristics of the aquifer at the site studied and the exploitation methods, no long-term threat to the water quality is foreseen.
Latest Quaternary and Holocene paleoceanography of the eastern Baffin Island continental shelf, Canada: benthic foraminiferal evidence
Authors: Osterman Lisa E. , Nelson Alan R.
Published: April 2011

Foraminiferal zones, radiocarbon ages on shells, and corrected ages on pretreated organic sediment from four cores from the eastern Baffin Island continental shelf suggest a three-stage deglacial to postglacial history (Late Wisconsin to Holocene). The earliest sediments in the cores contain foraminiferal species (Elphidium excavatum, Cassidulina reniforme, Islandiella helenae) indicative of distal glaciomarine environments that lasted at least several thousand years. An oceanographic change about 8500 years ago is indicated by a Melonis zaandamae zone in northern and central shelf cores collected from 200–800 m water depth. The presence of M. zaandamae in the north and its absence in the south suggest warmer and more saline postglacial water in northern Baffin Bay, whose influence became diluted with cooler coastal meltwater as the current flowed south along the Baffin Island Shelf. Sediments after 6000 years ago on the northern and central shelf are dominated by agglutinated foraminifera, suggesting dissolution of calcareous species. This dissolution event, which affected deeper water cores sooner than cores from the shelf, may be related to the influx of cold, CO2-rich water from the Arctic Ocean during the mid-Holocene. Thus, postglacial oceanographic changes in Baffin Bay appear first in deep northern waters; the lag time in the response to these changes in the shallower water on the shelf and to the south may have been as long as several thousand years.
Paleomagnetism and geochemistry of Carboniferous Sandwich Bay dykes from coastal Labrador
Authors: Murthy G. , Gower C. , Tubrett M. , Pätzold R.
Published: April 2011

Paleomagnetic, petrographic, and geochemical data are used to characterize a suite of dykes in the Sandwich Bay area, south of Cartwright, Labrador. These dykes are Carboniferous in age and their separate identity is indicated by the following: (i) distinct paleomagnetic signatures, (ii) homogeneous geochemistry, (iii) cross-cutting relations with other dated rock units in the area, and (iv) a whole-rock K–Ar date of 327 ± 13 Ma.The dikes have a soft present Earth's field component superposed on a stable magnetization at D = 325.5°, I = −26.9 °(N = 14, k = 91.6, α95 = 4.6°) with the corresponding paleopole at 16.2°N, 157.6°E (dp, dm = 2.8°, 5.2°). The stable magnetization is shown to be primary from baked contact tests. No Kiaman overprint is present. The paleopole determined for the dykes suggests emplacement of the dykes at equatorial latitudes during the Carboniferous times.
The age, chemistry, and tectonic setting of the Middle Proterozoic Moyie sills, Purcell Supergroup, southeastern British Columbia
Authors: Höy Trygve
Published: April 2011

Moyie sills comprise an extensive suite of basaltic rocks that have intruded Middle Proterozoic Purcell Supergroup rocks in southeastern British Columbia. The sills are spatially restricted to the Aldridge and Fort Steele formations in the lower part of the Purcell succession and are distinct from a suite of mafic sills higher in the succession. They may constitute up to 30% of a typical sequence but generally decrease in volume upsection as the abundance of thick-bedded A–E turbidites decreases. A number of the sills have textures and contact relationships that suggest they intruded unconsolidated or partly consolidated wet sediments.A U–Pb zircon Middle Proterozoic date of 1445 Ma from a coarse-grained sill is interpreted as being the minimum age of emplacement. Because the sills are penecontemporaneous with Aldridge sedimentation, this date defines the minimum age of deposition of lower and basal middle Aldridge rocks.Two distinct compositions of Moyie sills are recognized. Most are subalkaline, high-iron tholeiitic basalts, whereas others are alkaline basalts. The two different chemical trends are typical of volcanism in an incipient rift environment or in the early stages of continental rifting. This supports a model for deposition of Belt–Purcell rocks in a large, subsiding intracratonic basin formed by Middle Proterozoic rifting.
Siliceous sponge communities, biological zonation, and Recent sea-level change on the Arctic margin: Ice Island results
Authors: Wagoner Nancy A. Van , Mudie Peta J. , Cole Flona E. , Daborn Graham
Published: April 2011

Bathymetric profiles, bottom-camera photographs, surface-sediment samples, and biological samples were obtained through a 44 m long hydrohole in the Canadian Ice Island as it drifted over the Canadian polar margin from western Ellesmere Island to Meighen Island. Continuous bathymetric profiles show a 300 km wide shelf with a narrow, dissected, shallow (< 200 m) inner shelf and a deep (300–800 m), sloping outer shelf. Extensive areas of siliceous sponge communities are present on the seafloor beneath the polar pack ice on the central shelf. A clear biological zonation is evident: above 130 m, large living sponges support a diverse benthic community and form reef mounds up to 10 m high; from 130 to 150 m, there are few living sponges, but extensive mats of sponge spicules are present; from 150 to 300 m, there are few, small living sponges, and radiocarbon dating of mud-covered spicule mats indicates that formerly extensive sponge communities have died during the past 500–2000 years. This zonation may reflect a relative-sea-level depth increase of ~40–60 m during the past 1000 years. Alternatively, the zonation may indicate a 20–30 m upward shift in the warm Atlantic water layer during the past 500–1000 years, perhaps reflecting global climatic warming. The study of factors that determine the distribution and growth of the modern polar sponge communities has important implications for understanding the paleoecology of Paleozoic demosponge–bryozoan bioherms in the eastern Canadian Arctic Islands.
The Sept-îles layered mafic intrusion: geophysical expression
Authors: Loncarevic B. D. , Feininger Tomas , Lefebvre Denis
Published: April 2011

Eighty-eight percent of the Cambrian Sept-Îles layered mafic intrusion, possibly the second largest on Earth, lies under the estuary of the St. Lawrence River. A marine geophysical cruise in 1986 tied together all earlier gravity surveys and added gravity measurements along 1100 km of new track lines.The following results were based on the 1986 survey and other geophysical data. The Sept-Îles layered mafic intrusion is nearly circular in plan and about 80 km in diameter. It is funnel shaped and some 5.6 km thick at its centre. It has a volume of about 20 000 km3 and is composed of gabbro and allied rocks in a layered series (nearly [Formula: see text] of the total bulk), ultramafic rocks in a lower series (about [Formula: see text]), and gabbro, anorthosite, and potassium-feldspar-bearing rocks in a transitional and upper series (about [Formula: see text]). Roof rocks on the intrusion may have been restricted to a consanguineous volcanic cap.The Sept-Îles intrusion is located at the northwestern end of a reentrant of the North American continent where Appalachian tectonostratigraphic zones are offset dextrally by 400 km. Emplacement of the intrusion may be related to the initial opening of Iapetus. The southeastern border of the intrusion is downwarped and overlain by a rocky cover 8 km thick. The cover may be composed of Taconian nappes thrust northwestward at the reclosing of Iapetus. If this is so, Logan's line crosses the Sept-Îles layered mafic intrusion about 10 km southeast of its centre.
Tunicate spicules and their syntaxial overgrowths: examples from the Pleistocene Ironshore Formation, Grand Cayman, British West Indies
Authors: Jones Brian
Published: April 2011

Pleistocene limestones of the Ironshore Formation, deposited approximately 125 000 years ago, contain stellate tunicate spicules that are morphologically similar to those of the modern Trididemnum strigosum Kott, 1980 from Australia. The aragonite spicules, up to 0.1 mm in diameter, have a 1–4 μm diameter nucleus formed of anhedral crystals (<1 μm long), surrounded by radially disposed composite crystals that have a pseudohexagonal cross section. The spines, which have a hexagonal cross section, are formed of subcrystals.During diagenesis the tunicate spicules were modified by (i) the development of concentric laminae of aragonite needles (up to 2.2 μm long and 0.2 μm wide), which are tangential to the outer surface of the spicule but randomly orientated in the tangential plane, and (or) by (ii) syntaxial aragonite overgrowth of the crystals in the spicule. If the spicules were surrounded by densely packed mud, no overgrowths occurred. Conversely, significant overgrowth occurred if the spicules were surrounded by loosely packed mud or faced into an open cavity. Where completely encased by syntaxial overgrowths, the original spicule is difficult to recognize. Interruptions in the growth of the syntaxial overgrowths produced concentric growth rings, which are marked by a physical discontinuity or a thin zone of concentrically arranged aragonite crystals. Some spicules are encased by two or more zones of aragonite overgrowths with well-developed growth lines. Available evidence suggests that the syntaxial overgrowths on the tunicate spicules probably developed soon after deposition of the sediments while they were still in a marine setting.The recognition of tunicate spicules in ancient limestones is important because they provide evidence of soft-bodied animals that are rarely documented from ancient faunas despite their abundance in modern oceans. Although superficially similar to inorganically precipitated aragonite spherulites and Microcodium, the tunicate spicules can be recognized by careful consideration of their morphological attributes.
Evidence of Paleogene sedimentation on Graham Island, Queen Charlotte Islands, west coast, Canada
Authors: White James M.
Published: April 2011

The palynomorph taxa Ctenosporites eskerensis, Pesavis tagluensis, and Tilia spp. demonstrate that an unnamed sedimentary unit in the Union Port Louis well and float from Mud Bay Creek, Skidegate Inlet, British Columbia, most likely fall in the age range Early Eocene to Early Oligocene. These two localities, 66 km apart, have yielded the oldest Tertiary sediments yet confirmed on the Queen Charlotte Islands or in the Queen Charlotte Basin. The sediments are apparently continental. They exhibit high thermal maturity, which may be due to local volcanism, plutonism, or regional subsidence. The relationship of the Paleogene sediments to the late Tertiary Skonun Formation has not been determined.
Depositional environments of the Early Proterozoic Espanola Formation, Ontario, Canada
Authors: Bernstein L. , Young G. M.
Published: April 2011

The carbonate-rich Espanola Formation forms part of the Huronian Supergroup, deposited in Early Proterozoic time between about 2.5 and 2.1 Ga ago. The Espanola Formation overlies glacigenic diamictites of the Bruce Formation and is gradationally overlain by fluvial sandstones of the Serpent Formation. In the southern part of the outcrop belt, the Espanola Formation comprises a lower limestone member, a middle siltstone member, and an upper heterolithic member. These rocks record what may be the first marine incursion in the early Huronian and perhaps indicate a pre-rift phase of sedimentation. The limestone and siltstone members reflect low-energy conditions with sporadic influxes of fine-grained siliciclastics and carbonate debris from turbidity or storm-derived currents. Deposition took place subtidally, either in a shallow-marine setting or in a large lake, following the end of Bruce glaciation. Deposition of the coarser grained heterolithic member took place in higher energy environments, dominated by shallow-marine tide and storm processes.In the study area, most carbonate is detrital in origin. Paleocurrents suggest a northerly source. The restricted nature of the basin, postglacial warming, and shallower marine conditions could have been factors in carbonate precipitation.
Central Superior Province geology: evidence for an allochthonous, ensimatic, southern Abitibi greenstone belt
Authors: Jackson S. L. , Sutcliffe R. H.
Published: April 2011

Published U–Pb geochronological, geological, and petrochemical data suggest that there are late Archean ensialic greenstone belts (GB) (Michipicoten GB and possibly the northern Abitibi GB), ensimatic greenstone belts (southern Abitibi GB and Batchawana GB), and possibly a transitional ensimatic–ensialic greenstone belt (Swayze GB) in the central Superior Province. This lateral crustal variability may preclude simple correlation of the Michipicoten GB and its substrata, as exposed in the Kapuskasing Uplift, with that of the southern Abitibi GB. Furthermore, this lateral variability may have determined the locus of the Kapuskasing Uplift. Therefore, although the Kapuskasing Uplift provides a useful general crustal model, alternative models of crustal structure and tectonics for the southern Abitibi GB warrant examination.Thrusting of a juvenile, ensimatic southern Abitibi GB over a terrane containing evolved crust is consistent with (i) the structural style of the southern Abitibi GB; (ii) juvenile southern Abitibi GB metavolcanic rocks intruded by rocks having an isotopically evolved, older component; and (iii) Proterozoic extension that preserved low-grade metavolcanic rocks within the down-dropped Cobalt Embayment, which is bounded by higher grade terranes to the east and west.
Geometry and kinematics of Wager shear zone interpreted from structural fabrics and magnetic data
Authors: Henderson J. R. , Broome J.
Published: April 2011

The Wager shear zone (WSZ) is characterized by progressive bending of northeast–southwest-trending aeromagnetic anomalies to the right as they merge with east–west-trending anomalies characterizing the shear zone. This feature indicates dextral net shear. Mapping of abundant and diverse asymmetrical structural fabric elements within the shear zone where it is well exposed along the south coast of Wager Bay, northwestern Hudson Bay, consistently confirmed dextral shear sense.Pervasive, dextral shear-zone mylonites were deformed by folds with hinges parallel to the shear direction (a folds), as well as by discrete, conjugate sinistral and dextral mylonitic shears. To form a folds in mylonites it is necessary for the mylonitic fabric to rotate out of a stable orientation in the plane of shear and flattening and also to rotate about an axis parallel to the shear direction, for which we have no general explanation.We conclude with the speculation that the WSZ is a strike-slip fault related to terminal collision of the Archean plate of Ungava with the Archean plate to the north marked by the 1.8 Ga Sugluk suture.