bluuebunny/crossref_metadata_2025 huggingface dataset:
THE MICHIKAMAU ANORTHOSITIC INTRUSION, LABRADOR
Authors: Emslie Ronald F.
Published: April 2011

The Michikamau Intrusion is a large, unmetamorphosed anorthositic mass lying within the broad belt of anorthositic bodies extending from southeastern Ontario to Labrador. Potassium–argon biotite dates place the time of crystallization of the intrusion at approximately 1 400 million years ago.The main rock units of the intrusion are leucotroctolite, anorthosite, and leucogabbro; essential minerals are plagioclase, olivine, clinopyroxene, and orthopyroxene. The bulk of the plagioclase falls in the range An52–An62 and olivine in the range Fo60–Fo70. The rocks are remarkably fresh and free from secondary alteration products.A number of features characteristic of large, layered basic plutons are present in the Michikamau Intrusion. The chilled margin has the composition of olivine basalt. However, the bulk composition of the mass is highly feldspathic, thus leading to the proposition that the basaltic liquid was heavily charged with plagioclase crystals. Cumulate structures and textures indicate that bottom accumulation of crystals may have played an important part in the solidification and differentiation of the intrusion.The course of differentiation of the magma was toward extreme iron enrichment with the development of ferrous-rich dioritic, granodioritic, and syenitic rocks as end products. It is unlikely that water played an important role in the crystallization of the intrusion.
SECULAR VARIATIONS IN THE 14C CONCENTRATION OF DOUGLAS FIR TREE RINGS
Authors: Dyck Willy
Published: April 2011

Measurements of the 14C concentration in a Douglas fir from Vancouver Island indicate a maximum variation of 44‰, during the past 1 100 years. The magnitude and trend of these variations are similar to those observed by de Vries (1958) in oak from Germany and by Willis et al. (1960) in sequoias from California, confirming earlier observations that atmospheric mixing of CO2 takes place rapidly on a large scale.14C measurements of successive annual growth rings from the piths of two firs (346 years and 1 142 years old) show no variations beyond those attributable to the statistical counting error of ± 6‰. Thus, cyclic variations in sunspot activity and (or) climate, if present during these intervals, did not affect the 14C concentration in the biosphere appreciably.A mechanism, based on a climate-sensitive carbon pumping rate of the biosphere coupled with the temperature-dependent oceanic CO2 content is postulated to explain, qualitatively, the observed short-term (150 years or less) and long-term (1 000 years or more) 14C variations in the land biosphere. Short-term fluctuations are directly proportional to temperature because variations in the carbon fixation rate lead to a pulsating CO2 content of the atmosphere. Long-term changes are inversely proportional to temperature because large quantities of carbon, normally stored in deeper regions of the ocean, are exchanged between biosphere and hydrosphere.
SECONDARY FAULTING: I. THEORETICAL ASPECTS
Authors: Chinnery M. A.
Published: April 2011

The results of two previous papers by Chinnery published in 1963 and 1964 are used to calculate the distribution of stress that is present after the formation of a strike-slip fault. The pattern obtained shows that although the initial stress is reduced over most of the length of the fault, there are strong concentrations of shear stress near the ends. It is therefore suggested that secondary faulting is due to these end effects, and patterns of likely modes of secondary faulting are shown. The geological implications of these results are discussed in another paper, on the geological aspects of Secondary faulting.
SECONDARY FAULTING: II. GEOLOGICAL ASPECTS
Authors: Chinnery M. A.
Published: April 2011

A secondary fault is defined as a fracture which arises as a direct result of movement on a master transcurrent fault. Some previous approaches to the study of secondary faulting are discussed, and fallacies in the arguments of McKinstry (1953) and Moody and Hill (1956) are pointed out. The effect of movement on a fault is to reduce the initial shear stress everywhere except in the vicinity of the ends of the fault, where it causes complex additional stresses (see first paper in this series on the theoretical aspects of secondary faulting). Thus it is proposed that secondary faulting is an end effect of a master shear movement, and on this basis six major modes of secondary faulting, labelled types A to F, are described. The usefulness of these results in the analysis of fault systems is illustrated by applying them to the Alpine, San Andreas, and Mac Donald faults. In each case it is possible to predict or explain the curvature, location, and sense of the secondary faults in the area. In addition, the development of the master fault may be traced by locating the ends of the shear zone at various times in the past.
SUBSOLIDUS PHASE RELATIONS IN THE SYSTEM Ag–Sb
Authors: Somanchi S.
Published: April 2011

Phase relations were determined in the Ag–Sb system through the temperature range 500° to 300 °C to permit a better understanding of the origin of certain silver ores and to provide a base for the study of more complex sulfosalt systems. The Sb-rich solvus for the ε phase (Ag6 ± xSb) at 500°, 450°, 350°, and 300 °C occurs at 18.2, 17.75, 17.75, and 17.7 weight percent Sb, respectively. The Ag-rich solvus of the ε′ phase (dyscrasite) occurs at 22.5% Sb at 500 °C and 22.9% at 450°, 400°, 350°, and 300 °C. The Sb-rich solvus of this phase occurs at 27.2% Sb at 500°, 450°, 400°, and 350 °C. Therefore the atomic silver to antimony ratio ranges from nearly 4 to 3, and the formula may be written Ag7 ± xSb2. An order–disorder transition of ε′ to a third phase, ε″, reported to occur at about 440° to 449 °C, was not observed. The compositions of the solid solutions relate to high angle X-ray powder reflections through the following functions: for ε phase, d = 0.000150x + 0.79743, and for ε′ phase, d = 0.00160x + 0.76608, where d is the specific interplanar spacing in Ångstroms and x is the weight percent antimony.
A GEOCHRONOMETRIC STUDY OF THE SUPERIOR PROVINCE NEAR RED LAKE NORTHWESTERN ONTARIO
Authors: Purdy J. , York Derek
Published: April 2011

Nine samples of granites and gneisses collected along a 125 mi traverse running south from Red Lake have been analyzed in a Rb–Sr whole-rock study. It is concluded that an isochron may meaningfully be drawn through points representing these sample on a Nicolaysen (1961) plot. A slope equivalent to an age of 2.45 ± 0.10 b.y. results. If the gneisses represent the residue of an ancient crust then the Rb–Sr data yield little evidence of this and the effect of the Kenoran orogeny is clearly the dominant feature. K–Ar and Rb–Sr dating of biotites separated from two of the gneisses indicates that the area has been more mildly affected by a later metamorphism.
POTASSIUM–ARGON DATES OF BASIC INTRUSIVE ROCKS OF THE DISTRICT OF MACKENZIE, N.W.T.
Authors: Leech Alice Payne
Published: April 2011

Samples were taken from diabase dykes and related contact rocks and from a differentiated intrusive body of the District of Mackenzie in the Yellowknife–Prosperous Lake area, the Lac de Gras area, the Point Lake area, and the Tree River – Coronation Gulf area. In addition, several samples were taken from basic intrusions of Ontario, and some of the results obtained from these are included.Radiometric dating by the potassium–argon method indicated at least four periods of diabase dyke intrusion in the Slave Province of the Precambrian shield about 2 200–2 400 m.y. ago, 1 900–2 100 m.y. ago, 1 100–1 200 m.y. ago, and 600–700 m.y. ago. Scatter in the radiometric dates prevents recognition of other possible events by use of the whole-rock method, where the age of intrusion is older than Middle Proterozoic.Chemical and petrologic studies were carried out in conjunction with the radiometric dating. Precise determination of potassium proved difficult; in most cases, a best value for each sample was selected from the results of three independent determinations. There is some suggestion of an increase in the potassium content of diabase dykes in the Canadian shield throughout Precambrian time. Alkali–silica ratios show that all of the diabase dykes studied belong to the world-wide tholeiitic magma type.
WHOLE-ROCK AGE AND INITIAL 87Sr/86Sr OF VOLCANICS UNDERLYING FOSSILIFEROUS LOWER CAMBRIAN IN THE ATLANTIC PROVINCES OF CANADA
Authors: Fairbairn H. W. , Bottino M. L. , Pinson Jr. W. H. , Hurley P. M.
Published: April 2011

A Rb–Sr whole-rock age study has been carried out on three volcanic groups which underlie fossiliferous Lower Cambrian in the Atlantic provinces of Canada. Isochron ages of these three, and their initial 87Sr/86Sr ratios, are shown below.[Formula: see text]The Harbour Main group unconformably underlies younger formations which include the Bull Arm.The contemporaneity of the Coldbrook, Fourchu, and Bull Arm groups, predicted on field evidence, is confirmed by the age study, as is also the greater age of the Harbour Main. However, the isochron ages (500 m.y, average) of the three younger groups are at least 10% low by current time-scale standards for the base of the Cambrian. As all the data, show considerable departure from strict linearity, it is suggested that small and variable diffusion of Rb into the rocks has occurred, thus scattering the points and lowering the ages.Initial 87Sr/86Sr at the level 0.704—0.707 suggests for these magmas a subsialic source, which if not in the upper mantle, is at least in the lower part of the crust.
THE PURPOSE OF GLACIER MAPPING
Authors: Schytt Valter
Published: April 2011

As an introduction to the Symposium on Glacier Mapping and for the purpose of providing a basis for further discussion, the requirements in various types of glacier maps are differentiated. Most maps of glaciers are not made specifically for glaciologists but as part of a general geographical survey program. It is very important that glaciologists define their most urgent requirements, remembering that glaciers normally cover a fairly small percentage of a total area to be mapped. Standardized symbols would be good; standardized content might be better. The glaciological content has to be adapted to the scale of the map and to the needs of specialized research.
SOME NOTES ON GLACIER MAPPING AND ICE MOVEMENT
Authors: Haefeli R.
Published: April 2011

Since the time of Agassiz, 1840, the Unteraar Glacier has maintained its rôle as a focus of glaciological research for mapping, seismic sounding, glacier movement, and hydrology. Variations of the velocity of the Unteraar Glacier with ice thickness and time are presented and discussed. The new map of the Aletsch Glacier at the scale of 1:10 000 enables the author to demonstrate the extent to which detailed mapping of the surface features of a glacier facilitates the study of surface velocity.
INFRARED MAPPING OF THERMAL ANOMALIES IN GLACIERS
Authors: Poulin Ambrose O. , Harwood T. A.
Published: April 2011

All-season aerial reconnaissance of the Arctic has been advanced with the development of airborne, infrared scanners. The utility of such equipment for detecting and studying the progression of thermal anomalies of glaciological interest is discussed with reference to specific examples of imagery obtained during three seasons on Project "Bold Survey" under conditions of both daylight and darkness. Where possible, comparisons are made between infrared thermal imagery and conventional aerial photography.
TEST OF CONTOUR ACCURACY ON A PHOTOGRAMMETRIC MAP OF ATHABASCA GLACIER
Authors: Paterson W. S. B.
Published: April 2011

An independent survey of the positions and elevations of 59 surface markers set in the lower part of Athabasca Glacier permits assessment of the accuracy of contours on a large-scale map of the glacier. The root mean square difference between the elevation at each marker as determined from the survey and from the map was 49 cm. This is an upper limit to the standard error of the contours. It is less than three times the theoretical error and about 15% of the contour interval.
Rb/Sr AGE AND GEOLOGICAL SETTING OF THE HOLYROOD GRANITE, SOUTHEAST NEWFOUNDLAND
Authors: McCartney W. D. , Poole W. H. , Wanless R. K. , Williams H. , Loveridge W. D.
Published: April 2011

The Precambrian Holyrood granite of southeastern Newfoundland is of particular geological interest, because of its tectonic position on the easternmost exposed flank of the Appalachian mobile belt. Although previously considered to have been emplaced during the Grenville orogeny, this granite yields a Rb/Sr isochron age of 574 ± 11 million years (m.y.). Tectonic and sedimentary events that followed the granite emplacement, and that preceded the deposition of nonconformably overlying fossiliferous Lower Cambrian strata, are believed to have required at least 15 m.y. Consequently, a tentative maximum age of 560 ± 11 m.y. is proposed for the base of the Cambrian in this region.
NEPHELINE GNEISSES OF THE WOLFE BELT, LYNDOCH TOWNSHIP, ONTARIO: I. STRUCTURE, STRATIGRAPHY, AND PETROGRAPHY
Authors: Appleyard Edward C.
Published: April 2011

The Wolfe Belt is a sequence of banded gneisses characterized by nepheline and other minerals with abnormally high sodium contents. Two main units can be recognized. On the north side of the belt and extending along its entire mapped length are leurocratic feldspathic gneisses, generally nepheiine-bearing. These gneisses form a unit up to 350 ft thick and over 4 miles long in which also occur bands of amphibolite, crystalline limestone, and quartzite. The southern half of the belt consists of calc-silicate gneiss up to 230 ft thick with intercalated horizons of metamorphic pyroxenite and 'iron-formation'.These lithotogical units are interlayered and contain within them well-developed banding, which is attributed to relict supracrustal layering. Nepheline may be present in all of the units except the quartzite, but its distribution is irregular, although influenced to a large degree by the stratigraphy. The species and compositions of the associated mafic minerals are related to the nepheline content of the rocks as well as to the bulk rock composition.The Wolfe Belt is interpreted as being of metasedimentary origin, the parent rocks having been metasomatized during the Grenville orogenic period. The only igneous phase present is leucocratic alkali–syenite, which intrudes the nepheline gneisses and modifies them.
DISTRIBUTION AND ORIGIN OF PARENT SOIL MATERIALS IN PART OF THE OTTAWA AND BONNECHERE RIVER VALLEYS, ONTARIO
Authors: Burger D.
Published: April 2011

In an area of about 1 500 square miles, ten parent material classes were recognized on the basis of texture (grain-size) and petrography (base in rock fragments and carbonate content relate to nutrients available to plants). The distribution of materials in various landforms was related to mode, direction, and distance of transport from their bedrock sources by glaciation and by subsequent inundation by the post-glacial Champlain Sea.An ancient shoreline in the Ottawa Valley at 500 to 520 ft probably marks an important stage of the Champlain Sea.An improved basis for mapping soil series comes from such an understanding of the geologic events responsible for the distribution of parent materials.
GEOLOGY AND PALEONTOLOGY OF PLEISTOCENE DEPOSITS IN SOUTHWESTERN MANITOBA
Authors: Klassen R. W. , Delorme L. D. , Mott R. J.
Published: April 2011

Sediments containing fossils and organic material occur within Pleistocene deposits underlying multiple tills in the Duck Mountain and Riding Mountain Uplands of southwestern Manitoba. Pollen, ostracods, and mollusks within the sediments on Duck Mountain indicate a cool–warm–cool climatic sequence, which began more than 37 760 years B.P. Bones of a ground squirrel (Citellus) and vole (Microtus) were recovered from an intertill silt on Riding Mountain. Grass associated with the bones was dated as more than 31 300 radiocarbon years B.P.The sediments may be correlative with some of the beds of the recently redefined Port Talbot interstade in the Lake Erie region, though it is inferred they are older and correlative either with an early Wisconsin interstade or with the Sangamon interglacial in the mid-western United States.
GLACIAL FEATURES OF THE NORTH-CENTRAL LAKE SUPERIOR REGION, ONTARIO
Authors: Zoltai S. C.
Published: April 2011

The surficial glacial features and glacial events of a 13 000 square mile area in northern Ontario are described, based on field work and study of aerial photographs. Ice-laid and glaciolacustrine materials suggest a complex history of stationary ice fronts and glacial lakes during deglaciation. Lakes in the Lake Nipigon and Lake Superior basins inundated large areas. Post-Minong lake stages in the Superior basin intruded far to the north, dammed by ice at the largest moraine, the Nakina. The northern part of this lake was later separated from the post-Minong lake by differential uplift and was named Lake Nakina. After the withdrawal of the ice, Glacial Lake Barlow–Ojibway occupied the northeastern part of the area, and much of it was later overridden by the last glacial readvance. Stratigraphic correlations with radiocarbon dates suggest that the Nakina moraine was built some 9 400 years ago, and that the last glacier ice disappeared before 6 390 years ago.
THE ATHABASCA VALLEY ERRATICS TRAIN, ALBERTA AND PLEISTOCENE ICE MOVEMENTS ACROSS THE CONTINENTAL DIVIDE
Authors: Roed M. A. , Mountjoy E. W. , Rutter N. W.
Published: April 2011

The Athabasca Valley Erratics Train contains a variety of low- to medium- grade metamorphic rocks, the most abundant of which is talcose schist, with lesser amounts of garnet schist and biotite–quartz schist. This erratics train occurs in and west of the Athabasca Valley west of Edson, Alberta. It is probably a late stage deposit of the same glacier that carried and deposited the Erratics Train, Foothills of Alberta. The metamorphic erratics were incorporated into a glacier that originated in the northern part of the Monashee Mountains and Premier Range of British Columbia. This ice movement is also recorded by numerous U-shaped valleys, which extend across the Continental Divide. Thus, during a brief period in late(?) Wisconsin time, the Cordilleran ice in the Rocky Mountains of the Jasper National Park area was partly derived from west of the Continental Divide and the Rocky Mountain Trench. These data agree with the inferred ice movements shown on the 1958 Glacial Map of Canada.
MANICOUAGAN, QUEBEC, PALEOMAGNETIC RESULTS
Authors: Robertson W. A.
Published: April 2011

The remanent magnetization of dacitic material from Manicouagan, Quebec, was examined. Laboratory thermal studies support the view that viscous buildup in situ was small and secondary components insignificant. A pole position of 89 °E., 57 °N. is calculated from the mean direction of 6 sites. Comparison with other North American paleomagnetic poles points to a possible Triassic age for the formation of the material.
EARTHQUAKE EPICENTERS AND STRAIN RELEASE IN CANADA
Authors: Milne W. G.
Published: April 2011

Earthquake epicenters from a catalogue of the earthquakes in Canada, the Northern United States, Alaska, and the Aleutian Islands are plotted on maps. This catalogue contains the instrumentally located earthquakes within the years 1900 to 1960, and the historical record of earthquakes that have been felt along die St. Lawrence River from 1534, Accumulated values of strain release are computed for each unit area (1° × 1°) on the earth's surface. Contour maps are drawn from these. The areas of greatest activity are along the Aleutian arc, in Alaska, along Canada's west coast, and in the St. Lawrence Valley. It isshown that within a 100-year period there may be an earthquake near magnitude 71/4 below Quebec City, and near Vancouver Island. Areas of lesser activity are shown.
HUDSON BAY CRUSTAL SEISMIC EXPERIMENT: TIME AND DISTANCE DATA
Authors: Hobson George D.
Published: April 2011

A crustal refraction experiment was shot in August 1965 in Hudson Bay as part of a comprehensive survey encompassing the fields of geophysics, geology, and oceanography. Nine university and government crews participated. Eight stations were located on the periphery of the bay, while telemetering sonobuoys were monitored at a central location in the bay. Good quality data were obtained from 41 shots. All preliminary data pertaining to participants, instrumentation, shot times and distances, travel times, etc. are tabulated in this report.
AEROMAGNETIC AND GEOLOGICAL INTERPRETATION OF A SECTION OF THE APPALACHIAN BELT IN CANADA
Authors: Bhattacharyya B. K. , Raychaudhuri B.
Published: April 2011

Studies were made of total field aeromagnetic data over an area covering a section of the Appalachian belt in eastern Canada. This area is bounded by latitudes 45 °N and 47°40′ N and longitudes 62°30′ W and 67 °W. The residual magnetic values were filtered analytically in order to accentuate the effects of regional tectonic trends in the area. The second vertical derivative values were evaluated for outlining the contacts of magnetized geological formations with a reasonable degree of accuracy. Results of the analysis of the Bouguer anomaly map for the area seemed to correspond well with the tectonic trends indicated by the aeromagnetic data. Sixty-five anomalies were chosen from the residual and filtered maps to determine the following parameters of the causative bodies: (1) intensity of polarization; (2) direction-cosines of the polarization vector; and (3) depths to the top and bottom of the bodies.The picture of the pre-Carboniferous basement, as inferred from aeromagnetic data, is that of a valley and ridge configuration characterized by a series of subparallel, elongated basement blocks with relative vertical displacements. The basement blocks are bounded by major fault systems, known or inferred, mostly of pre-Carboniferous age. These blocks are aligned mostly in the direction of major tectonic trend in the area. The details of subsurface Basement topography are discussed on the basis of the results of interpretation of aeromagnetic data. Most interesting of all is a belt of high magnetic intensity running roughly in a NW–SE direction over the Gulf of St. Lawrence and Prince Edward Island. It has been suggested that this belt is caused by a pre-Taconic topographic high, or alternatively, by a pre-Carboniferous basement high bounded by fault zones subparallel with the fault system under the Cabot Strait.
DENSITY-FRACTION X-RAY ANALYSIS: A NEW TECHNIQUE OF MODAL ANALYSIS OF ROCKS
Authors: Erdosh George
Published: April 2011

Point counting, the present and often unreliable method of modal analysis of rocks, is unsatisfactory for many rock types. An instrumental technique that could be routinely performed by a technician is highly desirable. X-ray powder diffraction has been critically evaluated for this purpose and was found to be a suitable instrumental method when combined with density separation. A practical technique is thus proposed in which the rock powder is split into three density fractions by heavy-liquid separations and each fraction is quantitatively analyzed for its major constituents by X-ray diffraction. Altogether 28 minerals are considered, which are constituents of most igneous and many metamorphic rocks, and calibration curves are given for ten of these. With one exception, the precision was found to be reasonably good for the minerals determined. The accuracy of the technique could not be tested satisfactorily. The analytical time varies from 2 to 4 man-hours per sample depending on the rock type. Although the study is somewhat preliminary and the proposed technique is incomplete, it already shows some obvious advantages over point counting for many rock types.
GEOTHERMOMETRY FROM CHANGES IN STRESS BIREFRINGENCE AROUND INCLUSIONS IN GARNET DURING HEATING TO 900 °C
Authors: Hutchison W. W.
Published: April 2011

An examination of stress birefringence around inclusions in 8 garnets during heating to 900 °C, suggests that some changes in birefringence are due to fit-misfit relationships of inclusions in garnet.Some garnets appear to have behaved as natural bombs, which have carefully preserved the misfit relationships since crystallization of the combination of detached or partly detached inclusion in garnet. This combination can be used to determine the temperatures of fit at room temperature for various inclusions in garnet. Using certain approximations the intersection of curves of fit (on a P-T plot) can be employed to determine possible temperatures and pressure of formation of the garnet. In addition the changes in birefringence around inclusions of quartz reveal whether the garnet (or quartz inclusion) crystallized above or below the α-β quartz inversion.This technique is limited chiefly by the lack of P-V-T data on minerals, yet it can be applied to determine possible minimum and maximum temperatures and pressures of formation of garnets or their inclusions.
Postglacial rebound in Arctic Canada: similarity and prediction of uplift curves
Authors: Andrews J. T.
Published: April 2011

Twenty-one uplift curves from Arctic Canada indicate a similar proportional response through time. The time/altitude relationship can thus be expressed as a per cent of uplift within a specific time period. A graph of the results is a smoothly decelerating curve. Uplift curves can be approximated by the formula: U = A(1 − it)/(1 − i) where U is uplift, t is time with 0.0 years being the moment of site deglaciation, i is a constant for Arctic Canada equal to 0.677, and A varies with time and amount of recorded uplift. Tables and a figure are presented so that uplift curves can be predicted on the basis of: (1) elevation of the marine limit; and (2) date of site deglaciation. A comparison between Arctic Canada, east Greenland, and Fennoscandia indicates that relaxation times for a comparable period (10 × 103 years) are 2.5, 1.7, and 3.0 × 103 years respectively. Velocities derived from uplift curves allow the amount of residual uplift to be calculated. A figure of 100 m is suggested for a sector of Hudson Bay.
Identification of Saskatchewan Gravels and Sands
Authors: Stalker A. MacS.
Published: April 2011

'Saskatchewan gravels and sands' is the name used for numerous, widely scattered deposits of gravel and sand found on the Canadian Prairies. These deposits represent the final phase of deposition by preglacial rivers before the first Pleistocene ice-sheet disrupted regional drainage. In the past, Saskatchewan gravels and sands have been identified chiefly by their absence of stones from the Canadian Shield and position below the drift in buried valleys or on low ground. These remain the basic criteria. Sole dependence on them, however, has resulted in extraneous deposits being called Saskatchewan. Such misidentifications cannot be eliminated entirely, but their number can be greatly decreased by use of additional checks. These include intensive study of each deposit and its topographic position, and establishing that there was both an adequate source for the gravel and sand contained in it and competent means of transporting that material from source to present site. In addition, the valley containing the deposit must have formed an integral part of the preglacial drainage system, its cross-section and longitudinal profile must have resembled those of a typical preglacial valley, and there must not have been any competing valley that could have carried the local, preglacial drainage more efficiently.
Preliminary studies of intertidal sand bodies in the Minas Basin, Bay of Fundy, Nova Scotia
Authors: Swift D. J. P. , McMullen R. M.
Published: April 2011

Sand winnowed from bay-floor deposits and eroded from sea cliffs in the Minas Basin has been swept into a series of intertidal sand-body complexes. Continuous seismic profiles show that these are plano-convex or tabular sand masses up to 30 m thick and 30 km long. Two types of complex are present: the Windsor Bay complex is a tidal delta type, while the Cobequid Bay complex represents a braided type. The Windsor Bay complex consists of a main channel, flanked by two levee-like lateral bars, capped by a lunate cross-bar. The complex is localized by the phase difference between the retarded estuary tide and the tide of the main bay. The Cobequid Bay complex consists of rhomboid to oval bars, whose blunt ends face the incoming tide, which are defined by interlacing channels.Tidal current velocity data measured over the complex indicate two regimes: a high-water, sheet-flood phase and a low-water, channel phase. On the surface of the bars, first-order sandwaves show mainly flood asymmetry while second-order sandwaves show mainly ebb asymmetry. The flood asymmetry of the bars and larger sandwaves is a consequence of the skewed nature of the tidal cycle. Sand transport in the Minas Basin appears to be eastward, along both shores.
Infrared absorption spectra of mineral matter in saxicolous lichens and associated mosses
Authors: Dormaar J. F.
Published: April 2011

Saxicolous lichens and associated mosses, and their weathered and fresh rock zones, were collected from a number of locations. All material was treated with hydrogen peroxide and infrared spectra of the remanining mineral matter were obtained.Spectra of the mineral matter obtained from the lichens and mosses differ generally from those of the substrata. There is evidence that quartz and dioctahedral structures could be products of weathering of rocks by lichens and mosses. It is likely that saxicolous lichens obtain at least part of their minerals from the substrata. There is no indication of the presence of magnesium or of carbonates in the peroxidized material of lichens obtained from calcareous or dolomitic substrata. Peroxidation of the organic tissues leads, in the presence of calcium, to the formation of calcium oxalate; the relative intensities of the bands related to calcium oxalate, in particular those at 1325 and 780 cm−1, may be used to assess the amount of calcium present. It is suggested that this change in intensity may be a useful criterion in evaluating the transformation of Chernozemic humic acids to Podzolic humic acids in soil.
Notes on late-glacial palynology and geochronology at St. Hilaire, Quebec
Authors: Terasmae J. , Lasalle P.
Published: April 2011

A palynological study supported by radiocarbon dates of late-glacial sediments at St. Hilaire, Quebec, indicates that the southern part of the St. Lawrence Lowland was deglaciated prior to 12 500 years B.P. The late-glacial episode comprises several climatic fluctuations: a probable early cool interval (northern boreal) more than 12 500 years B.P.; a relatively colder interval (tundra) about 12 500 years B.P., followed by another cool interval from about 12 000 years B.P. to about 10 000 years ago. Another relatively cold episode may have occurred about 11 000 years ago. The new studies extend the previously available palynological record in the St. Lawrence Lowland back in time by about 2000 years and include the Champlain Sea episode.
A geochemical profile of the Swan Hills Reef
Authors: Cameron E. M.
Published: April 2011

Over four hundred samples were taken from cores that form a vertical plane section through the Swan Hills Reef, an important oil-bearing reservoir in the Devonian rocks of west-central Alberta. Quantitative determinations for eight elements were made on the samples by direct-reading emission spectrometry. The resulting chemical data were treated by R-mode factor analysis techniques, including rotation to oblique solutions and the computation of factor scores. The distribution of the different factors within the reef was then determined by computing trend surfaces for the scores. Factors with low eigenvalues and even specific factors were found of considerable use for interpreting the data.Dolomite in the reef appears to be derived mainly from high-magnesian calcite of possible algal origin that was formed on the windward side of the reef. Sr held in calcite as a solid solution impurity shows a primary trend to depletion in the organic framework facies that margins the reef. This is caused by greater diagenetic leaching of these rocks. Secondary variation of Sr may indicate periods when the reef was elevated above sea level and underwent subaerial weathering. Vertical variation of Mn and Fe held in solid solution in calcite appears to be related to tectonic changes in the region.
Radiometric age of the volcanics at Arisaig, Nova Scotia, and the Ordovician–Silurian boundary
Authors: FullAgar Paul D. , Bottino Michael L.
Published: April 2011

Volcanics from the Arisaig-Antigonish district of northeastern Nova Scotia underlie fossiliferous Lower Silurian (Lower Llandovery) sediments. The minimum geologic age of the volcanics is Early Silurian, and the maximum geologic age probably is post-Early Ordovician. Twelve whole-rock samples of the volcanics were analyzed for rubidium, strontium, and strontium isotopic composition. The best estimate of the age of these twelve samples is 430 ± 15 m.y.; this is a maximum age or close to a maximum age for the Ordovician–Silurian boundary. This age plus the authors' results for the Silurian-Devonian boundary indicate that the Silurian Period in northeastern North America may have been shorter than generally has been estimated. Additional Silurian-age volcanics are being analyzed.
An ancient landslide along the Saguenay River, Quebec
Authors: Lasalle Pierre , Chagnon Jean-Yves
Published: April 2011

The largest landslide (8 square miles) yet reported in eastern Canada is described and two 14C dates (560 ± 90 years B.P. 420 ± 90 years B.P.) believed to be related to the time of its occurrence are presented
The Precambrian geochronology of Australia
Authors: Compston W. , Arriens P. A.
Published: April 2011

K–Ar and Rb–Sr age-determinations made on Australian Precambrian rocks up to 1967 are summarized and discussed. On present sampling, and subject to its possible bias, we distinguish broad periods of acid magmatism and high-grade metamorphism between: (I) 3050–2900 m.y., (II) 2750–2600 m.y., (III) 1900–1700 m.y., and (VI) 1100–950 m.y., plus relatively shorter periods between (IV) 1550–1500 m.y., (V) 1400–1350 m.y. and (VII) 700–650 m.y. Isolated granitic bodies were emplaced outside these periods; extensive acid volcanics in the range 2000–2200 m.y. may signify important plutonic activity of this age not yet discovered.With similar qualifications, we distinguish six Precambrian sedimentary successions of different ages and of varying geographical extent. Although the radiometric controls on their separate durations are not yet satisfactory, the overlap between different successions in time appears to be small or absent, and, in contrast with previous impressions, the sediments may document only about half the total time between the Cambrian and 3100 m.y.
The Precambrian problem in younger orogenic zones: An example from Japan
Authors: Matsumoto Tatsuro , Yamaguchi Masaru , Yanagi Takeru , Matsushita Susumu , Hayase Ichikazu , Ishizaka Kyoichi , Kawano Yoshinori , Ueda Yoshio
Published: April 2011

We have examined some of the presumed Precambrian basement metamorphic and granitic rocks in Japan, through radiometric dating as well as on field evidence, and have found that mineral ages of about 175 to 250 m.y. are abundant in the Hida area, northwestern part of central Japan, that a number of thrust rocks in southwestern Japan show ages of 400 to 450 m.y., and that the oldest of the measured samples is about or somewhat over 500 m.y. Little evidence is available to support a view that the Pre-Sinian rocks, if ever existent, have remained unaltered under such a polycyclic orogenic zone as that represented by Japan, although remnants of the youngest Precambrian to Early Paleozoic cycle can be detected.
Geochronology of stratified rocks of the Canadian Shield
Authors: Stockwell C. H.
Published: April 2011

In the Canadian Shield, four orogenies, each followed by a profound unconformity, serve to divide the succession into five natural time-stratigraphic units. These are named for convenience in mapping, description, and discussion. Rock units in type areas, rather than abstract time, form the basis for the classification. Isotopic dates place the geological units in a scale of years and are extremely valuable for the purpose of long range correlation.
Rb–Sr whole-rock and K–Ar mineral ages of rocks from the Superior Province near Kirkland Lake, northeastern Ontario, Canada
Authors: Purdy J. W. , York D.
Published: April 2011

A Rb–Sr whole rock investigation of two acid intrusive bodies in the Superior Province of the Canadian Shield have yielded isochrons corresponding to ages of 2.39 ± 0.08 b.y. and 1.73 ± 0.05 b.y. Additional K–Ar data on separated minerals from each of these intrusive bodies supports the Rb–Sr data. The existence of a dike-like intrusion of the 1.73 b.y. rock into the 2.39 b.y. rock is also inferred from the data.
Geochronology in the Lake Superior region
Authors: Goldich S. S.
Published: April 2011

During the past 10 years many radiometric ages have been determined on minerals and rocks in the Lake Superior region. The oldest known rocks are the granitic gneisses in the Minnesota River Valley, which have been dated at 3300 to 3550 m.y. ago. Both K–Ar and Rb–Sr methods have been applied to samples from a number of the metasedimentary formations in the region. The ages, however, appear to be the time of folding or of metamorphism rather than of deposition for which only limits or ranges can be given from the ages for associated igneous and metamorphic rocks.Although considerable progress has been made, significant uncertainties remain in the decay constants and in the analytical measurements. More serious problems, however, are geologic ones, such as the effects of metamorphism and of weathering on the parent–daughter nuclide ratios. Both analytical and geological considerations must enter into any proposal for a time classification of the Precambrian.A three-fold division of the Precambrian with time boundaries at 2600 and 1800 m.y. serves well for the Lake Superior region. In addition, the Keweenawan igneous activity is well dated at approximately 1100 m.y. ago. Terms such as Keweenawan, Huronian, and others are best used locally, and time units of a Precambrian classification that might have world-wide utility should not be tied closely to geographic localities. A single radiometric method, as for example K–Ar largely on micas, is not a satisfactory basis for a classification.
Isotopic ages from the Appalachians and their tectonic significance: Discussion
Authors: Dennis J. G.
Published: April 2011

Geological field relationships demonstrate that the principal orogeny in the Northern Appalachians was the Acadian orogeny in Devonian time, and that events culminating in the Late Ordovician (Taconic) disturbance were precursors of the Acadian orogeny in the Appalachian geotectonic cycle.
Advances in marine geophysical research of continental margins
Authors: Worzel J. Lamar
Published: April 2011

Geophysical data available for the continental margins of North America, South America, Africa, and Europe are examined and summarized. Seismic reflection profiling provide much detail of the uppermost sedimentary cover; seismic refraction data delineate the broad outlines of the upper crustal layers; and gravity data restrict the choices of the deeper crustal structure and that of the upper mantle.Conclusions about the variability of the sedimentation at the various continental shelves, slopes, and rises are given. The transition zone between continental and oceanic structure is restricted to a narrow zone varying between 50 km and 300 km in width for various coasts. This transition zone is localized in the region of the 2000 m isobath for all the coasts studied. The continental margins are generally in isostatic equilibrium as a whole, although departing from this equilibrium somewhat, expecially in the transition zone.
Structure and development of transition zones between the continents and oceans
Authors: Beloussov V. V. , Kosminskaya I. P.
Published: April 2011

A set of geological-geophysical data provides a good basis for the recognition of two basic types of marginal zones: Atlantic and Pacific. The analysis of the tectonics and deep structure of the crust allows us to characterize their development in time, proceeding from a basic, well-grounded conception that beginning with the Cretaceous Period processes of crustal subsidence were dominant in the marginal zones of both types. In connection with the different structure of margins on the continental side and their correspondingly different mechanical properties, i.e., strength and monolithic quality, it is evident that the effects of crustal subsidence in different zones should have different manifestations.The Atlantic type of margins is characterized on the continental side by the platform regime, and the development of the marginal zones was here accompanied by the subsidence of the marginal part of the pre-Mesozoic foundation with an increase of its tilt towards the ocean. The M boundary in this zone is observed to have a steep rise of the scarp type, approximately 15 km for every 100 km. The inhomogeneity of the foundation structure and the possible irregularity of the processes of its subsidence in certain areas resulted in the formation of small plateaus detached from the shelf. The zones of the Atlantic type were evidently unconnected with considerable reduction of land, and they are mainly located within the boundaries of the pre-Mesozoic shelf.The margins of the Pacific type are characterized by another mechanical regime, which develops on the background of largely differing geosynclinal structures of continents. Sinking of large blocks is here followed by their disintegration into smaller blocks, as well as by volcanism with which the formation of island arcs of the second type and of the accompanying troughs is associated, etc. Starting with the Neogene in the zones of this type, the areas of the ocean expanded and in place of land vast marginal seas were formed with a thinned continental and suboceanic crust.The connection between the primary mechanical properties of the earth's crust of the marginal zones and the character of structures which evolved as the result of its subsidence is only one side of the phenomena causing the difference in the types of margins. As the subsidences of the crust are succeeded by its regeneration under the influence of the processes in the mantle, it might also be supposed that in the Atlantic zones with platform conditions these phenomena developed more regularly, while in the Pacific zones in the conditions of the geosynclinal state of the interior the same process had a more complicated and diverse development.
Active regions of the southwest Pacific
Authors: Evison F. F.
Published: April 2011

The southwest quadrant of the Pacific, from southern New Zealand to central New Guinea, contains eight distinct active regions of the asymmetric type (i.e. continental margins and island arcs). These regions vary widely in size, shape, and geodynamic character. Four of them face towards and four away from the Pacific Ocean; hence the concept of a circum-Pacific active belt is only partly applicable. The area includes some of the most intensely active features known, such as the deep-focus seismicity of the Tonga region and the intermediate-focus seismicity of the New Hebrides region. There are none, however, of the great curved structures that are typical of the north and northwest Pacific areas. The southwest Pacific is a severe testing-ground for hypotheses concerned with large-scale processes and structures in the upper mantle and crust.
Transcontinental crustal sections of the U.S.S.R. and adjacent areas
Authors: Beliayevsky N. A. , Borisov A. A. , Volvovsky I. S. , Schukin Yu. K.
Published: April 2011

Transcontinental sections of the earth's crust and Upper Mantle from the Kuril Islands to the Carpathians, and along other principal directions, in all about 15 000 km long, show the following features:(1) The depth of an asthenosphere horizon agrees well with the position of a high-conductivity layer in the Upper Mantle.(2) Hypocenters of earthquakes are located in fault zones. In the zone of the Kuril Island arc, they plunge into the Upper Mantle to depths of hundreds of kilometers, dipping towards the continent.(3) Boundary velocities along the Mohorovičić discontinuity are not dependent on its depth, for they are always in the range 8.0–8.2 km/s; velocities within the crust are correlated with the depths of layers; in the roots of high mountains a layer of 7.5–7.8 km/s has been distinguished near the base of the crust.(3) The crustal thickness in folded areas is in a certain accordance with the altitude of the surface of the earth's solid cover, with Bouguer anomalies and amplitudes of neotectonic movements. It varies from 8 km in margin areas of the Pacific Ocean basin to 60 km in the Tien Shan. Average crustal thicknesses within the platforms are in the region of 40 km, increasing to 50 km in the southern outlying areas of the East-European platform and to 46 km in areas of recent tectonic activity within the Turanian and Siberian Platforms.(4) In deep depressions, internal and outlying seas, the crustal thickness is reduced, and 'granite' layer (6.0–6.5 km/s) is absent. Mesozoic formations of the Far East and adjacent zones of transition from the Pacific Ocean to the continent are distinguished by reduced thicknesses. In Alpine formations the 'basalt' layer dominates over the 'granite' layer.(5) Subhorizontal crustal stratification complicated by deep faults has been found everywhere. Plicate geosynclinal folding is not reflected in deep crustal structures.(6) Temperature of the platform folded basement is mainly related to thickness and composition of the sediments.The transcontinental sections provide a clearer idea of the relationship between anomalous geophysical fields and deep and shallow crustal structures than is given in corresponding maps.
The superstructures of two synthetic pyrrhotites
Authors: Fleet M. E.
Published: April 2011

A new, hexagonal superstructure of pyrrhotite, with a = 2A, c = 3C (where A and C are respectively the a and c parameters of the NiAs-type sub-cell), is reported from a quenched, synthetic iron sulfide preparation containing pyrrhotite in equilibrium with pyrite. The X-ray diffraction record for it is similar to those for previously reported analogous superstructures, but exhibits reflections in positions equivalent to positions of extinction in the latter. In addition, a hexagonal superstructure with a = 2A, c = 4C is reported from a less-sulfur-rich, quenched, synthetic pyrrhotite.
The Mid-Atlantic Ridge near 45& deg;N. III. Bald Mountain
Authors: Aumento F. , Loncarevic B. D.
Published: April 2011

Metamorphosed and metasomatized basalts, and unmetamorphosed equivalents, were recovered from the steep slopes of Bald Mountain, a north–south elongated seamount lying 60 km west of the Median Rift Valley at 45° N. Block faulting and uplift of the seamount, together with the removal by submarine erosion of extrusive rocks capping the seamount, have resulted in the exposure of the more deep-seated metamorphosed horizons along the fault scarps.The block-faulted nature of Bald Mountain, indicative of brittle fracturing of the upper crustal layers of the Mid-Atlantic Ridge, may be a result of the low ocean floor spreading rates implied from age determinations and magnetic anomaly patterns at 45 °N.