bluuebunny/crossref_metadata_2025 huggingface dataset:
CAPULISPORITES LONGIPROCESSUM N. SP., A POSSIBLE MARKER PLANT SPORE FROM THE BELLY RIVER FORMATION (CAMPANIAN) OF ALBERTA, CANADA
Authors: Hills L. V. , Jensen E.
Published: April 2011

Capulisporites longiprocessum, a new species of plant spore, is described and illustrated from the Belly River formation of westcentral Alberta. A preliminary palynological study of the Belly River, Edmonton, and Paskapoo formations suggests that this spore is restricted to the Belly River formation. This conclusion is strengthened by the earlier studies of Campbell (1962), who indicated that spores of this type were confined to strata of pre-Edmonton formation age.
STRUCTURAL GEOLOGY OF PRECAMBRIAN ROCKS SOUTH OF BANCROFT, ONTARIO
Authors: Best Myron G.
Published: April 2011

Structural analysis of Precambrian metamorphic rocks south of Bancroft, Ontario, has disclosed fold structures in lithologic layering, which are examined on the working hypothesis that two distinct generations are present. Folds of the first system, in the southern part of the mapped area, are fairly open, nearly recumbent, and plunge gently eastward, whereas folds of the second system, found in the northern part of the area, are tighter, with steep southeast-dipping axial planes and variably oriented axes. Uniformly steep stratiform foliation and linear mineral segregations, characterizing an extensive terrain between the so-called Hastings basin and the Haliburton–Hastings highlands, seem to have evolved by progressive tightening of the second folds and transposition of the layering parallel to the axial planes. In the area studied, the distinction between the highlands and the basin is basically one of predominant rock type, with progressive changes in structural character evident between the two. As formerly reported, the distinction involved strongly contrasting structural characteristics, with intervening zones of faulting.This part of the Grenville province is structurally very complex, and considerably more data and analysis are needed to unravel the tectonic history.
AEROMAGNETIC STUDY OF THE CHURCHILL–SUPERIOR BOUNDARY IN NORTHERN MANITOBA
Authors: Kornik L. J. , MacLaren A. S.
Published: April 2011

A regional aeromagnetic study of northern Manitoba suggests adjustments in the position of the Churchill–Superior boundary. This proposed boundary is correlated to a narrow, continuous magnetic low that changes direction at its northern end, from a northeast trend to an east–west trend that approximately parallels the 56° N. latitude line.The date pattern of age determinations chiefly supports the position of the proposed boundary. Comparison of aeromagnetic patterns to the geology establishes their close correlation. Aeromagnetic anomalies appear to be chiefly produced by near-surface material and can be correlated with the surface geology. A comparison of the gravity patterns to the aeromagnetic and geologic patterns establishes the apparent independence of the gravity patterns to the other two. The gravity anomalies appear to be produced by larger scale density contrasts which are not correlative with near-surface material. A deeper, crustal source of the gravity anomalies fits the evidence better.
THE BASAL SEDIMENTARY ROCKS IN SOMERSET ISLAND, N.W.T.
Authors: Tuke M. F. , Dineley D. L. , Rust B. R.
Published: April 2011

In northwest Somerset Island quartz sandstones of the Aston formation and dolostones of the overlying Hunting formation rest unconformably on metamorphic basement rocks. Except for stromatolites and trace fossils the formations are unfossiliferous, and their age has been interpreted as Proterozoic by previous authors.The Aston sandstones pass conformably upward into the Hunting dolostones, which are conformably overlain by Ordovician strata. A similar succession with Middle Cambrian trilobites at the base occurs on Boothia Peninsula. It is therefore suggested that the Aston and Hunting formations comprise a Palaeozoic succession continuous with the fossiliferous Ordovician rocks. This hypothesis does not appear to be incompatible with regional interpretations of Proterozoic–Palaeozoic relationships.The sedimentary structures and petrology of the Aston sandstones suggest that they were derived from the basement rocks and deposited in a shallow marine environment. Sedimentary structures and stromatolites in the Hunting dolostones show that they were laid down in coastal lagoons and tidal flats.
CARTOGRAPHIC REPRESENTATION AND SYMBOLIZATION IN GLACIER MAPPING
Authors: Ewing Karen J. , Marcus Melvin G.
Published: April 2011

In glacier cartography, as in all mapping, questions of convention and standardization have long plagued cartographers. National and international efforts at standardization have generally failed. To assess the styles, techniques, and status of glacier representation, several hundred maps of glaciers and related features were examined and evaluated. As a result it is suggested that there is room for innovation and that greater attention be devoted to the following problems: (1) color symbolization, (2) perception of symbols and color by map users, (3) inclusion of more symbolic information on medium-scale maps, and (4) effects of automated cartography on representation techniques.
EXPERIENCE IN GLACIOLOGIGAL MAPPING OF ICE SHEETS AND MOUNTAIN GLACIERS
Authors: Avsiuk G. A. , Vinogradov O. N. , Kravtsova V. I.
Published: April 2011

As a result of the I.G.Y.–I.G.C. programs, the whole complex of glacier processes has received particular attention in the USSR. This has led to the development and perfection of cartographic methods in the study of glaciers. Three main lines in glacier mapping are being followed in the USSR in the preparation of (a) general geographical maps of glacierized areas, (b) special glaciological maps, and (c) glacier atlases. The characteristics of the various types of maps are described, and details are given on their preparation and on the representation used for natural features and glacier processes. New applications of cartographic methods to glaciological investigations are indicated.
BISON OCCIDENTALIS LUCAS FOUND AT TABER, ALBERTA, CANADA
Authors: Trylich C. , Bayrock L. A.
Published: April 2011

An articulated incomplete skeleton of a mature male Bison occidentalis Lucas was found in alluvial sand on the uppermost terrace of the Oldman River near Taber, Alberta. Description of the bones and some comparison with ox and horse are made. Two radiocarbon ages of 10 500 and 11 000 years coupled with invertebrate fossil and pollen analyses show that at this time the area was free of ice and that parkland vegetation was well established in Southern Alberta. The pebble chopper found in association with the skeleton points to human occupation of the area at that time.
STRUCTURAL ANALYSIS OF THE QUEENSWAY FOLDS, OTTAWA, CANADA
Authors: Norris D. K.
Published: April 2011

The Queensway folds are an anticline–syncline pair in layered limestone and shale of the Ottawa Formation in the Ottawa – St. Lawrence Lowlands. They are parallel, flexural-slip folds with horizontal axes trending northwest, parallel to the surface trace of the Gloucester fault.Five principal fracture subpatterns were recognized in the fold-pair, caused by at least four geometrically distinct stress fields. The principal stress directions at failure for all five subpatterns coincided, moreover, with the three orthogonal fabric axes, and the maximum principal stress was either parallel or perpendicular to the fold axes and to the Gloucester fault.Slickenside striae on bedding and on fractures at an angle to bedding indicate two principal kinematic patterns in the fold-pair; the one arises from motion in the deformation plane as a consequence of the folding and the other from strike-slip motion perpendicular to that plane as a consequence of displacement on the Gloucester fault.Slickensides indicate that each bed was free to move relative to adjacent ones during folding and that the fundamental structural unit in flexural-slip folding is the bed. Model studies support the field data and indicate that the sense and magnitude of interbed slip in any structural position is dependent upon an integral of conditions throughout the fold-pair and that the fundamental fold unit is the anticline–syncline pair.
A NEW FAUNA OF EARLY ORDOVICIAN GRAPTOLITES FROM ST. MICHEL, QUEBEC
Authors: Erdtmann Bernd-Dietrich
Published: April 2011

A locality 12 miles downstream from the type locality for the Levis Formation has yielded a new genus, Stellatograptus, and three variants of Clonograptus sarmentosus (Moberg) as well as other forms, suggestive of the fauna of the Hagastrand Member of the Lower Ordovician section at Oslo, Norway. Biometrical data on the dominant forms are tabulated and extensive revision for C. sarmentosus is offered.
EVIDENCE BEARING ON THE ORIGIN OF THE BELLEORAM STOCK, SOUTHERN NEWFOUNDLAND
Authors: Ermanovics I. F. , Edgar A. D. , Currie K. L.
Published: April 2011

The Belleoram stock of homogeneous adamellite is a shallow, late-orogenic intrusion emplaced in arkosic conglomerates, granite, intermediate to basic lavas, and clastic sedimentary rocks. The intruded rocks range in age from Cambrian to Late Devonian. Salic dykes and minor faults cutting the stock represent the closing phases of orogenic activity in this area.Structural, petrographie, and chemical data indicate that the stock is of magmatic origin. Differential assimilation of the host conglomerate and shales may have locally modified the composition of the crystallizing magma. Field observations and modal analyses show that arkosic conglomerates near the stock have been altered to rocks of granitic composition. The margin of the stack has been basified near contacts with shale. Xenoliths of shale have been altered to compositions approaching that of their host. Hydrothermal experiments show that under appropriate conditions the magmatic vapour phase could transport soda, potash, alumina, and silica, in amounts sufficient to explain the observed compositional variation.These results suggest that under suitable conditions combined processes of autometasomatism and assimilation may be an important factor in granitization and basification at the margins of shallow intrusions.
EXPERIMENTS ON DENSITY AND TURBIDITY CURRENTS: III. DEPOSITION OF SEDIMENT
Authors: Middleton Gerard V.
Published: April 2011

Turbidity currents were formed by releasing suspensions of plastic beads (density 1.52, median diameter 0.18 mm) from a lock into a horizontal water-filled flume. Graded beds were formed; the mechanism of deposition was studied by motion photography and the size grading by 150 size analyses.Deposition of sediment took place behind the head even at a time when there was no deceleration of the head: the greater part of the thickness of the bed was deposited during a period of rapid decline in velocity of flow within the body of the current. The mechanism of deposition and the type of grading differed for beds deposited from suspensions with concentrations less than and greater than about 30% by volume. Low concentration suspensions formed 'distribution grading' in which all percentiles showed vertical grading and at least the coarser half of the distribution showed lateral size decrease away from the gate. High concentration suspensions formed 'coarse-tail grading' in which there was almost no lateral size variation and the vertical grading was shown only by the coarsest few percentiles (except at the top of the bed).In high concentration flows the bed did not accumulate layer by layer, as it did in low concentration flows, but was deposited first as an expanded 'quick' layer, which was deformed by shearing and waves produced by the entrained water flowing over the still plastic bed.In both types of graded beds the sorting coefficient (standard deviation of the logarithm of the settling velocity) decreased upward within the bed, and to a lesser extent also laterally away from the gate. The skewness reached a maximum near the center of the bed and became negative at the top.
ILE RONDE BRECCIA, MONTREAL
Authors: Clark T. H. , Kranck E. H. , Philpotts A. R.
Published: April 2011

The breccia occupying most of St. Helen's Island and Ile Ronde was originally considered to be sedimentary, later volcanic, and is now attributed to diatreme action. It contains fragments of all local formations including the Precambrian basement and also Devonian limestone blocks.Recent excavations on Ile Ronde have shown fracture zones in the breccia filled exclusively with fragments of the adjacent Utica shale. More important is a new type of breccia consisting of sub-rounded masses of Precambrian quartzites and other rocks (but no anorthosite) held in a matrix of olivine diabase of Monteregian affinities.
ISOTOPIC DATING OF THE GUICHON BATHOLITH, B.C.
Authors: White Wm. H. , Erickson G. P. , Northcote K. E. , Dirom G. E. , Harakal J. E.
Published: April 2011

The Guichon batholith in central southern British Columbia is composed of seven granitic phases, together with genetically associated porphyritic dykes and cataclastic breccia bodies. Four of the granitic phases form a concentrically zoned pattern, the geologically youngest phase being in the center and the oldest on the periphery. The batholith as a whole intrudes volcanic rocks of the Upper Triassic Karnian Stage and is unconformably overlain by Middle and Upper Jurassic marine sediments. Twenty-four samples taken for age determination by the potassium–argon method gave an arithmetic mean age of 200 m.y. with a standard error of the mean of ± 5 m.y. No loss of radiogenic argon subsequent to formation of the batholithic rocks is indicated by either geological or analytical observations. No difference of isotopic age could be detected between the geologically oldest and youngest rocks. The batholith originated by a complicated sequence of magmatic evolution, which was completed at a high crustal level during an interval of geologic time too brief to be detected by the analytical technique.
ARCHEAN VOLCANO-TECTONIC BASINS: FORM AND PATTERN
Authors: Goodwin A. M. , Shklanka R.
Published: April 2011

Two widely separated Archean volcano-sedimentary assemblages in the Superior Province of the Canadian Shield provide a composite view of Archean basin development. In both areas, a tectonically controlled distribution of felsic eruptive centers with associated differential subsidence leading to basin development is viewed as the prime cause of interrelated volcanic and sedimentary facies.The two areas contain similar, sequentially arranged, volcanic and sedimentary assemblages in which mafic-to-felsic volcanic sequences are associated with clastic sediments and iron-formations. The main periods of basin subsidence were broadly synchronous with widespread felsic eruptions. The development of steep transportation gradients promoted clastic sedimentation. Felsic pyroclastic piles provided local detrital sources.Banded iron-formations in both basins, attributed to volcanic exhalative origin, are transitional from volcanic to clastic sedimentary associations, thereby demonstrating essential contemporaneity of volcanism and sedimentation. Michipicoten iron-formations display a shore-to-depth arrangement of oxide, carbonate, and sulphide facies, which conforms to the basin configuration existing during the main period of iron and silica deposition.This analysis of Archean basin development and configuration in describing paleophysiographic relationships provides insight into early crustal history.
AN ESTIMATE OF THE CHEMICAL COMPOSITION OF THE CANADIAN PRECAMBRIAN SHIELD
Authors: Shaw D. M. , Reilly G. A. , Muysson J. R. , Pattenden G. E. , Campbell F. E.
Published: April 2011

A new estimate of the surface composition of exposed parts of the Canadian Precambrian Shield has been obtained, using samples of 122 rocks from northern Quebec–Ungava, 116 from Baffin Island, 116 from southwestern Quebec, 64 from northeastern Alberta, 18 from northern Saskatchewan, and 8076 from northern Ontario. Where feasible an interpenetrating replicate sampling design was used, with probability weighting by rock-type, analyzing both individuals and composites for trace elements, but only composites for major elements, A total of 385 triplicate spectrographic analyses and 48 major-element analyses were made.Regional differences between the six samples were detected; whether these also include secular variations could not be studied. The overall estimate follows:[Formula: see text]The major elements are similar to those found in granditorite, mica paragneiss, or graywacke, but the trace elements agree better with the last two only. Data for Th and U will follow later.The Precambrian Shield of Canada (and Fennoscandia also) contains more Si and K, and less Ti, Fe, Mn, Mg, and Ca than recent estimates of the whole crust of the earth.
FELDSPATHIC INCLUSIONS IN THE GARDAR IGNEOUS ROCKS OF SOUTH GREENLAND AND THEIR RELEVANCE TO THE FORMATION OF MAJOR ANORTHOSITES IN THE CANADIAN SHIELD
Authors: Bridgwater D.
Published: April 2011

Anorthosite xenoliths and plagioclase megacrysts occur in Gardar igneous rocks over an area of approximately 50 000 sq km in South Greenland. The anorthosite inclusions represent a top accumulate of labradorite, which crystallized at a relatively early stage from the developing Gardar magmas at depth, while the megacrysts are regarded as feldspars that remained suspended in their parent magmas for a considerable period at a later stage when the Gardar magmas had developed their dominantly alkaline character. The formation of anorthosite was a continuous process, which probably started about 1300 m.y. ago (the age of the earliest Gardar intrusions) and continued to about 1200 m.y.The Gardar anorthosites formed in the period immediately preceding the development of the Grenville metamorphic belt of the Canadian Shield. They are particularly relevant to the problem of the anorthosites in the Canadian Shield, since they provide evidence for the formation of anorthosites in pre-Grenville, post-Elsonian non-orogenic conditions. It is suggested that the main factor controlling the formation of the two main types of primary anorthosites—those of layered intrusions and those of the almost monomineralic Adirondack type—is the relative specific gravity of the plagioclase and its parent magma. In most layered intrusions, formed from uncontaminated basaltic magmas, the first-formed plagioclases are bytownitic and would sink in their parent magma. In contrast, in alkali provinces such as the Gardar and in orogenic environments where original basaltic magmas may have been contaminated, the first-formed plagioclase is commonly either labradorite or andesine. This will rise in either basaltic or dioritic magma. The separation of plagioclase by flotation from complementary mafic minerals provides a mechanism by which anorthositic rocks can form from basic magmas apparently unaccompanied by mafic layers.Once formed, anorthositic masses of this type would be extremely resistant and could survive several later plutonic episodes as large monomineralic masses in deep-seated mesozonal rocks or the upper katazonal rocks. In contrast the complementary layered mafic rocks would form layered masses in more deep-seated katazonal gneisses.
STRUCTURAL ANALYSIS MOKKA FIORD AND SOUTH FIORD DOMES, AXEL HEIBERG ISLAND, CANADIAN ARCTIC
Authors: Schwerdtner W. M. , Clark A. R.
Published: April 2011

Numerous piercement structures occur on the Queen Elizabeth Islands of the Canadian Arctic Archipelago. The exposed cores of these structures are composed chiefly of Pennsylvanian anhydrite, which may be underlain by rock salt. The cores are surrounded by Mesozoic rocks.A geometric analysis of two well-exposed domes on Axel Heiberg Island was made to learn whether the anhydrite behaved as an active source material or as a passive overburden during doming. Attitudes of bedding and lenticular limestone boudins were measured in both domes, and the axial traces of macroscopic folds were constructed.The flow pattern in the anhydritic domal cores corresponds to that predicted by model studies, suggesting that layered anhydrite behaved essentially as a source material for the domes. The South Fiord Dome is composed of three sub-cores, whereas the Mokka Fiord Dome rose as a single unit.During late stages of doming, large radial fractures developed in upper levels of the anhydrite cores. These fractures seem to correspond to the radial cracks in model overburdens, and indicate a change in the mechanical behaviour of anhydrite.
The Mid-Atlantic Ridge near 45° N. II. Basalts from the area of Confederation Peak
Authors: Aumento F.
Published: April 2011

Assisted by detailed bathymetric and bottom photographic coverage, a series of closely spaced samples of rock were taken by dredging along a traverse from the center of the Median Valley to the adjacent crest mountains on the Mid-Atlantic Ridge. The specimens show a gradation from tholeiitic to alkali basalts. Chemical variations, and the alkali content in particular, can be correlated with the depth of extrusion and with the topographic relationship of the volcanoes to the axis of the Median Valley.Although the basalts show considerable evidence of gravity-controlled crystal fractionation, the trends so established are evidently not responsible for alkali enrichment, but appear to be superimposed onto the more fundamental, continuous trend from tholeiitic to alkali basalts.
The optical absorption spectra of certain transition metal ions in muscovite, lepidolite, and fuchsite
Authors: Faye G. H.
Published: April 2011

The unpolarized optical absorption spectra of the sheet silicate minerals muscovite, lepidolite, and fuchsite have been examined. The spectra, interpreted on the basis of ligand field theory, indicate that all three minerals contain Fe3+ and possibly Ti3+ in octahedral sites. In addition, muscovite is shown to contain octahedrally coordinated Fe2+, lepidolite octahedral Fe2+ and Mn2+, and fuchsite octahedral Cr3+. No evidence was found for transition metals in tetrahedral sites.Some comments are made on the similarity of the spectra of certain of the transition metal ions in several classes of minerals. This leads to the speculation that the cations Fe3+, Mn2+, and Cr3+ may tend to 'mold' their immediate surroundings.
Contrasting Archean ultramafic igneous bodies in Dundonald and Clergue Townships, Ontario
Authors: Naldrett A. J. , Mason G. D.
Published: April 2011

A differentiated sill of ultramafic and gabbroic rocks in Dundonald and Clergue Townships (25 miles northeast of Timmins, Ontario) may be classed as a "stratiform intrusion", whereas several peridotite-pyroxenite lenses in the pillow lavas overlying the sill have characteristics that have not been reported in previously described ultramafic bodies.The sill was intruded as a nearly horizontal, conformable sheet, 4 × 2 miles in extent. It was differentiated as crystals settled from the cooling magma to form a 1000-ft thick basal layer of peridotite overlain by 500 ft of augite pyroxenite, 700 ft of gabbro, and 200 ft of granophyric gabbro. After solidification it was folded and faulted. The sequence of cumulus minerals and the cryptic layering throughout much of the sill are consistent with fractional crystallization models based on analogous experimental data.The lenses are generally stratibound, but are locally transgressive to the volcanic country rocks. The lenses range in surface extent from [Formula: see text] mile to 200 ft × 10 ft. Compositional zoning is parallel to the contacts; pyroxene increases in amount towards both contacts, in some places to the exclusion of olivine. The pyroxene-rich marginal parts and pyroxene-rich bands within the lenses are characterized by skeletal olivine, chromite crystals, and bundles of acicular pyroxene crystals, which indicate crystallization from a supercooled liquid. This conclusion is supported by the discovery of one pyroxene-rich sample that contains a calcic clinobronzite (Wo7.2En79.3Fs13.5) mantled by a sub-calcic augite with a higher percentage of iron than the core. The lenses are thought to have been injected as a mixture of olivine crystals and pyroxene-rich liquid into the volcanic sequence when this was still accumulating. Olivine became concentrated at the center of each lens as a result of flow. Rapid chilling of the marginal liquid occurred at the time of injection, giving rise to the skeletal textures.
Fossil vertebrates from the marine Cretaceous of Manitoba
Authors: Bardack David
Published: April 2011

The vertebrate fauna from the Upper Cretaceous of Manitoba is described. Of the 18 genera, 13 have not been recorded previously from this province. The vertebrate assemblage resembles that of the Niobrara Formation of western Kansas, but is noteworthy for the relative abundance of toothed birds.
Planktonic Foraminifera — new dimensions with the Scanning Electron Microscope
Authors: Bartlett Grant A.
Published: April 2011

Extremely fine, detailed morphological characteristics of micro-organisms, hitherto unavailable, can now be determined with the Scanning Electron Microscope. Morphological characteristics related to evolutionary sequences, specific, generic, and familial relationships will permit more natural faunal classifications and enable more accurate ecological and biostratigraphic correlations.
The quantitative determination of minerals in some metamorphosed volcanic rocks by X-ray powder diffraction
Authors: Bristol Calvert C.
Published: April 2011

A method is described for the quantitative X-ray powder diffraction determination of minerals in metamorphosed volcanic rocks of the greenschist, epidote-amphibolite, and amphibolite facies. In this method the intensity of the (111) diffraction for a powdered metallic Cu internal standard was compared to the intensities of selected diffractions for minerals of each facies.Graphs relating X-ray diffraction intensities to concentrations were prepared for actinolite, albite, almandine, anthophyllite, biotite, chlorite (omega: 1.59), diopside, epidote, hornblende, muscovite (2M1), plagioclase (An30), and quartz.Results using this method are within [Formula: see text] of those obtained by Rosiwal analysis.
Three computer programs for contouring map data
Authors: Smith F. G.
Published: April 2011

Three programs in FORTRAN IV language, to control an IBM 7094 computer and a CALCOMP plotter for contouring map data, are described briefly. In the first program there is no information on strike to bias the contouring. In the second program prior information on strike biases the contouring. In the third program any prior information on strike is recomputed and the result biases the contouring.
A thin till in West-Central Saskatchewan, Canada
Authors: Christiansen E. A.
Published: April 2011

A thin till, commonly 1 to 10 ft thick, forms the uppermost till in an area of more than 20 000 square miles in west-central Saskatchewan. The till, named herein the Battleford Formation, is gray to light olive-gray in contrast to the underlying pale olive and pale yellow till and stratified drift. The Battleford Formation was deposited about 20 000 years ago and is separated from the underlying older drift by a disconformity whose hiatus is about 15 000 years. These dates suggest that the weathering interval prior to the deposition of the Battleford Formation is Farmdalian and that the Battleford Formation is Woodfordian.
Metasomatic and Intrusive nepheline-bearing rocks from the Mbozi syenite-gabbro complex, southwestern Tanzania
Authors: Brock P. W. G.
Published: April 2011

The Mbozi Complex (20 × 8 miles) is situated on the Great North Road 15 miles east of the Tanzania–Zambia border. It is at least 743 million years old, and is emplaced in Ubendian Gneisses (1800 m.y.) along the northeastern flank of the Tunduma Rift.The oldest rocks in the complex are layered calcic gabbros, with cumulates of iron-rich pyroxenite and bytownite anorthosite. The basic rocks were faulted and deformed prior to the emplacement of alkaline rocks around the perimeter of the complex. The alkaline rocks are saturated with respect to silica near the ends of the complex, but are nepheline-bearing near the center. The larger masses of marginal syenite are magmatic intrusions.Within the basic rocks near the center of the complex is an elliptical zone of feldspathoidal rocks surrounding a core of unaltered gabbro. The rocks in this ring structure are heterogeneous, ranging in composition from slightly altered gabbro, through all intermediate compositions to ijolite, litchfieldite, and rutterite. They have well-developed concentric banding, but vary rapidly in composition and texture along and across strike. Contacts are gradational. The majority of the ring rocks appear to be metasomatized gabbros, but a few persistant, concordant bands of homogeneous litchfieldite are probably intrusive.Assuming no volume change and little change in color index, metasomatism of gabbroic rocks to produce the ring rocks would involve introduction of cations to the standard cell of 160 O ions in the proportion K5 – 9 Na21 – 27 Al−2 – +5 Si−5 – +11 P0 – +4 and removal of Ca14 – 21 Mg11 – 15 Fe2 – 4Ti1 – 2.It is concluded that the ring structure developed above a volatile-rich nepheline syenite, and that the metasomatism was effected by the volatile elements of that magma.
Autochthonous and allochthonous rocks in the Pistolet Bay area in northernmost Newfoundland
Authors: Tuke M. F.
Published: April 2011

Rocks outcropping in the northernmost part of the island of Newfoundland belong to two sequences, which are partly contemporaneous and very different in lithology. One sequence consists of Lower Cambrian sandstones and Lower and Middle Ordovician carbonates and shales. The other sequence consists of graywackes, volcanic rocks, and ultrabasic intrusions, which are, in part, early Ordovician. This latter sequence is interpreted as allochthonous because it is underlain by major low-angle faults and because of its strong facies contrast with the first sequence. The allochthonous rocks occur in three separate klippen.The trend of slickensides, attitude of folds, and deflection of beds at fault surfaces all indicate that movement along the low-angle faults that underlie the klippen was to the northwest. The klippen probably originated from an area 60 km to the southeast, which is on strike with similar rocks in north-central Newfoundland.It is suggested that the klippen moved by gravity sliding in late Middle Ordovician time.
Some orogenic episodes in South America by K–Ar and whole-rock Rb–Sr dating
Authors: Hurley P. M. , Melcher G. C. , Pinson Jr. W. H. , Fairbairn H. W.
Published: April 2011

Radiometric dating of basement rocks in South America by the M.I.T. geochronology laboratory has indicated the following thermo-tectonic episodes. The gneisses of the Imataca Complex of the Venezuela Guayana Shield are about 3000 m.y.; they have been intruded by igneous rocks of 2000 m.y. age. Ancient rocks between these age values have been found in the Bação Complex in Minas Gerais. The principal cratonic rocks of southeastern Venezuela, the Guianas, northern Brazil in the Amapa district, the coast region between Belém and São Luis, the region west of the Tocantins River, and in the São Francisco area near Salvador all show ages in the range 2000 ± m.y. The region in northeast Brazil represented by the Cariri orogenic belt shows an average Rb–Sr whole-rock isochron age value of 640 m.y. K–Ar age values in the Belo Horizonte district, Minas Gerais, show a metamoprhic overprint value of 500 m.y. A similar value is found in Colombia, east of the Macarena mountains.
Geochronology of the Yellowknife area, Northwest Territories, Canada
Authors: Green D. C. , Baadsgaard H. , Cumming G. L.
Published: April 2011

New whole rock Rb–Sr isochron data indicate that the Archean greenstones of the Yellowknife area are 2625 ± 160 m.y. old (λ87Rb = 1.39 × 10−11 yr−1). The thick, complexly folded sequence of volcanics and overlying sediments is intruded by two syntectonic to late tectonic batholiths (Rb–Sr isochron ages 2610 ± 58 m.y. and 2590 ± 90 m.y.) and a large irregular mass of muscovite granite (Prosperous Lake granite), which yields a mineral isochron age of 2575 ± 25 m.y.Low initial 87Sr/86Sr ratios (0.702–0.703) suggest that the late tectonic batholiths were unlikely to have formed by granitization of a great thickness of sediments beneath the greenstones (as has been suggested). Since the initial ratios of the volcanics and intrusive rocks are similar, the basalt–dacite association is probably the early extrusive expression of the subcrustal process that leads to the formation of quartz diorite–granodiorite batholiths. Appreciable sialic contamination need not be invoked. On the other hand, the Prosperous Lake granite ((87Sr/86Sr)0 = 0.712) may be the product of partial anatexis of the newly derived sialic crustal segment.
Major-element geochemistry of the Noranda volcanic belt, Quebec-Ontario
Authors: Baragar W. R. A.
Published: April 2011

The results of detailed mapping and sampling of two sections of Blake River Group volcanic rocks in the Noranda, Quebec region are presented and discussed. The Duparquet section, west of Lac Duparquet, crosses the north limb of a regional synclinorium where the assemblage is more than 40 000 ft thick. Continuity in upper levels of the succession is disrupted by folds, and the relative stratigraphic position of a sequence south of the folds near the synclinorium axis is uncertain but is interpreted as younger. The base of the section is the Porcupine-Destor fault. A subordinate section 40 miles to the east comprises a 12 500-ft thick assemblage overlying Kewagama sediments. Both sections were sampled at 400–500 ft stratigraphic intervals. The samples were analyzed for major elements by X-ray fluorescence and rapid chemical methods and the results checked by classical chemical analyses.Basalts and andesites are predominant rock types. Acidic volcanic rocks, prominent in assemblages a few miles east of the Duparquet section, may be represented by mixed acid–basic fragmental layers that occur in upper levels of the Duparquet section. Pumpellyite and prehnite are indicative of the low metamorphic grade of the rocks.Salient features of the chemistry of the Duparquet section are: (1) Al2O3 increases steadily with stratigraphic height throughout the lower 40 000-ft succession, the upper 15 000 ft of which are high alumina lavas, but is of normal content in the presumed higher levels near the synclinorium axis; (2) iron content and color index decrease markedly and MgO and TiO2 contents moderately with stratigraphic height, but all revert to more normal values in the supposedly higher sequence; (3) the remaining constituents show less distinct trends, but SiO2 and K2O are generally higher in upper levels of the section. In the subordinate section compositions are fairly constant and match those in the lower part of the Duparquet section. Noranda rocks resemble circumoceanic basalts except for markedly lower Al2O3 and K2O.Speculation on causes of the stratigraphic variations in composition are based on recent high-pressure studies. Increasing alumina content with stratigraphic height is attributed to a secular rise in the depth of magma generation from below about 35 km to above. Late production of acidic magmas may be due to eventual melting of parts of the crust.
A new cetacean from the Oligocene Sooke Formation of Vancouver Island, British Columbia
Authors: Russell Loris S.
Published: April 2011

Chonecetus sookensis, new genus and species, is based on an incomplete skull and parts of four vertebrae. It has a relatively elongate, tapering brain case, and a semicircular, depressed supraoccipital shield. It appears to be intermediate between archaeocetes and primitive odontocetes, but is tentatively placed in the Archaeoceti without reference to family.
The Devonian continental rocks of the lower Restigouche River, Quebec
Authors: Dineley D. L. , Williams B. P. J.
Published: April 2011

The Devonian continental rocks outcropping between Campbellton, New Brunswick and Miguasha, Quebec are regrouped on the basis of new stratigraphic information and the ages now suggested are thought to be in accord with new data. An Early or early Middle Devonian age for the La Garde Formation is apparent and a strong unconformity is noted at the base of this unit. The Pirate Cove Formation (Middle Devonian) is subdivided into five lithological units. The Fleurant and Escuminac Formations, of Late Devonian age, are included in the newly proposed Miguasha Group. The tectonic implication of the lithologies and the structural relationships of these rocks is a pulsatory sequence of uplifts.
Structure of the earth's crust of epi-continental seas: Caspian, Black, and Mediterranean
Authors: Neprochnov Yu. P.
Published: April 2011

Comparison of crustal structure of the deep basins of the Caspian, Black, and Mediterranean Seas indicates the similarities of the main characteristics: great Bouger anomalies, the absence of a 'granitic' layer, a thick sedimentary layer with a relatively smooth interface, aseismicity. However, each of the above-mentioned basins (or even different parts of one deep basin) has its peculiarities, which indicates a very complicated tectonic development of the entire Caspian–Mediterranean zone.
Continental and oceanic structure from the Oregon coast westward across the Juan de Fuca Ridge
Authors: Dehlinger P. , Couch R. W. , Gemperle M.
Published: April 2011

Seismic and gravity data were used to construct crustal and subcrustal sections from the Tufts Abyssal Plain, west of the coast of Oregon, to southern Idaho. Nearly the entire area appears to be in isostatic equilibrium. Mantle depths west of the Juan de Fuca Ridge, in eastern Oregon, and in southern Idaho are normal for the surface elevations or water depths at these locations, and the corresponding mantle densities and velocities appear to be 'normal'. The mantle under the Juan de Fuca Ridge and the Cascadia Basin (west of Oregon) is relatively shallow and its density appears to be below normal to a considerable depth. Two different mantle structures are considered that are consistent with the seismic and gravity data. Magnetic data were not found to be diagnostic in differentiation between these two structures.Across the continental margin the Mohorovicic discontinuity dips sharply under the continents, being at a typical depth of 18 km near the coast line. The discontinuity is relatively shallow under western Oregon (as has been proposed previously), and the corresponding mantle is described in terms of apparent velocity and density.
Bathymetric, magnetic, and gravity data from the continental margin of southwestern Africa
Authors: Simpson E. S. W. , Plessis A. du
Published: April 2011

The morphology of the continental margin between Cape Town (34° S) and Walvis Bay (23° S) is characterized by a broad, terraced shelf, separated from the slope by a poorly defined shelf break which deepens northward. A major belt of positive magnetic anomalies follows the upper slope, but is displaced in a right-lateral sense on to the continental shelf at 31° S, to the north of which it crosses a bend in the shelf break and again follows the upper slope. The gravity data is consistent with the normal edge effect associated with an isostatically compensated continental margin.
The subsidence of the North Sea area: A summary
Authors: Collette B. J.
Published: April 2011

Subsidence of the North Sea is explained as a result of a phase transition influenced by sediment loading, followed by differential movements resulting from the formation at depth of eutectic melts.
Lead- and sulfur-isotope ratios from the Great Slave Lake area, Canada
Authors: Robertson D. K. , Cumming G. L.
Published: April 2011

Lead- and sulfur-isotope ratios have been determined for some galenas and iron sulfides from two regions around Yellowknife, Northwest Territories. For the ore deposits, sulfur-isotope ratios are close to the meteoritic value or slightly positive. Lead-isotope ratios fall into two groups, one derived from a source with Th/U = 4.3 and μ = 9–11, and the other from a source with Th/U = 3.5 and μ = 9.0. The ratios fall on an anomalous lead line, which indicates one event of great antiquity (approximately 4000 m.y.), and another about 2800 m.y. ago.Other sulfide samples from areas around Great Slave Lake, primarily outside the ancient (2800 m.y.) Slave Province, indicate events at 2800 m.y. and 1550 m.y., the latter date probably representing the time of the last major tectonic event in the Slave Province. Sulfur-isotope ratios for these samples vary from +1‰ to −13‰ relative to the meteoritic value, suggesting that these leads may have been remobilized by thermal metamorphism, and recombined with crustal sulfur enriched in 32S.
Isotopic ages from the Appalachians and their tectonic significance: Reply to W. R. Church
Authors: Harper C. T.
Published: April 2011

The chronology of the Taconic orogeny is variously documented and can only be revealed through a careful consideration of all the chronologically pertinent evidence. The Late Ordovician post-metamorphic cooling event (uplift) revealed by K–Ar analysis of the Green Mountain schists was initiated 440 m.y. ago. Field evidence—the pre-Caradoc (445 m.y.) unconformity and the commencement of deposition of argillaceous sediments of Caradoc age—confirms this interpretation of the isotopic data.
Mineralogy and textural relationships of ores from the Whalesback Mine, northeastern Newfoundland
Authors: Kanehira K. , Bachinski D.
Published: April 2011

The Whalesback Mine is one of many copper deposits associated with Ordovician volcanic rocks in the Notre Dame Bay area, Newfoundland. The deposit consists of veins, pods, and disseminated sulfides localized within a highly chloritized shear zone cutting basaltic pillow lavas. Porphyritic dikes cut the shear zone, sulfide deposit, and the surrounding pillow lavas; all of the rocks, including the sulfide-rich rocks, have been regionally metamorphosed. Ore minerals, in decreasing order of abundance, include pyrite, chalcopyrite, pyrrhotite, sphalerite, mackinawite, pentlandite, magnetite, cubanite, galena, and ilmenite. Marcasite, covellite, and goethite are supergene minerals. Chlorite and quartz are the predominant gangue minerals. Muscovite, carbonates, sphene, albite, and epidote are minor constituents. Banding and streaking of sulfides in massive ores, crushed pyrite, and the local occurrence of pressure-shadow phenomena in the ore are indicative of shearing stress post-dating original sulfide ore formation. Present sulfide assemblages are compatible with relatively low temperatures and are the result of re-equilibration and internal reaction among the sulfides with decreasing temperature.
Geology of the terraces at Cochrane, Alberta
Authors: Stalker A. MacS.
Published: April 2011

The prominent terraces north of Bow River at Cochrane, Alberta, divide readily into an upper and a lower set. The three terraces of the upper set represent deltas built into lakes ponded in front of Laurentide ice. They were constructed between 19 000 and 15 000 years ago, when Classical Wisconsin glaciation was near its maximum. Due to the inhospitable conditions then prevailing, these upper terraces contain few or no fossils. During a warm interstade that followed, the glaciers shrank and Bow River deepened and enlarged its valley until ice readvance, about 12 000 years ago, stopped this phase of erosion. Before the glaciers in the Bow and its tributary valleys again retreated, more than 10 000 years ago, Bow River had deposited vast quantities of fill in its valley. Since then, the river has carved the five lower terraces from that fill and from the underlying bedrock.The valley fill is here named "Bighill Creek Formation". It is a valuable source of gravel and sand, and a prolific supplier of vertebrate fossils. Most of the latter come from a sand unit, here called "Clarke Pit Member", which extends throughout much of the formation. Radiocarbon dates indicate that the member is about 11 000 years old.
Correlation of Proterozoic strata in the northwestern Canadian Shield
Authors: Fraser J. A. , Tremblay L. P.
Published: April 2011

The Epworth and Goulburn Groups comprise the lowermost sequences of the Proterozoic strata exposed near the northern margins of the Slave (structural) Province of the Canadian Shield. Each group is at least 4600 m thick and underlies a distinct and separate area of not less than 13 000 sq. km.The many features common to the two groups indicate that they are correlative: (1) each lies unconformably on an Archean basement; (2) each is overlain unconformably and successively by kaolinitic sandstone, by dolomite, and by Coppermine River Group basalt and sediments; (3) each has argillite and quartzite near the base, interbedded argillite and limestone in the upper parts, and sandstone at the top; (4) each exhibits features characteristic of deposition in shallow water; (5) both occupy similar structural basins and show the same style of folding and faulting; (6) both are traversed by gabbro dikes and sills of similar age.Field relationships among the Proterozoic strata and the relation these strata bear to intrusive granite, dikes, and sills of known radiogenic age, define the Epworth and Goulburn Groups as of Aphebian age.
Crustal structure in Northwestern Ontario: Regional magnetic anomalies
Authors: McGrath Peter H. , Hall Donald H.
Published: April 2011

A regional aeromagnetic map, portraying the regional magnetic anomaly system in Northwestern Ontario west of longitude 92 °W and south of latitude 55 °N and extending westward into Manitoba to longitude 97 °W (with an additional block bounded by latitudes 54° N and 56 °N and longitudes 97° W and 102 °W) is presented. The map was prepared by multiple application of a two-dimensional smoothing operator applied to data digitized at 3 km intervals from the 1-inch-to-1-mile aeromagnetic map series published by the Geological Survey of Canada. Comparison was made with previous maps overlapping on portions of the area, which had been made by various techniques, including Fourier analysis, fitting of 6th-order polynomials, and photographic reduction. The general features of the anomaly system were found to be similar for all of these techniques. The regional anomaly system is found to be related in some cases to the thickness of the upper crustal layer (defined as lying above the Intermediate seismic discontinuity) and to structure within it, but not to the lower crustal layer or to the upper mantle.
Distribution, composition, and source of the White River Ash, Yukon Territory
Authors: Lerbekmo J. F. , Campbell F. A.
Published: April 2011

The White River Ash is a bi-lobate 1500 year old deposit occupying at least 6 cubic miles and covering some 125 000 square miles of southern Yukon and eastern Alaska. Sixty-six samples were collected at 5-mile intervals, principally along two traverses 120 miles apart across the main lobe, and subjected to X-ray fluorescence and petrographic analysis.The ash is a rhyodacite composed of glass (n = 1.502), andesine, hornblende, hypersthene, and magnetite. The average chemical composition is SiO2 = 67.4, Al2O3 = 15.1, TiO2 = 0.5, MgO = 2.0, FeO = 2.0, Fe2O3 = 2.2, Na2O = 4.1, K2O = 2.5 and CaO = 4.1, but there is a significant difference between the two traverses owing to the increase in glass relative to crystal components downwind.A synthesis of the distribution of the ash permitted the drawing of a 5 by 12 miles 'target' source rectangle in the St. Elias Range between Mts. Natazhat and Bona in Alaska. Aerial photographs revealed a suspect mound 0.4 miles in diameter beside the Klutlan Glacier. Access by helicopter showed the mound to be a flat cone of large White River pumice fragments. It is believed that the vent lies beneath the glacier next to the cone.