bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Contact Relationship of Charnockite and Biotite Gneiss at Bauchi, Northern Nigeria
Authors: Oyawoye M. O. 
Published: May 2009

AbstractPetrographic and chemical study of biotite gneiss and charnockite and the gradational transition zone between them suggests three probable modes of origin: (i) that charnockite was regionally widespread and the biotite gneiss was derived from it by retrograde metamorphism; (ii) that the charnockite represents a conformable intrusive igneous rock which with biotite gneiss was subjected to high-grade metamorphism; (iii) that the charnockite was derived from the biotite gneiss, by the introduction of some ferrous-iron rich juvenile solution.The latter is preferred by the author because it explains better the physical, chemical, and mineralogical characteristics of the charnockite.Evidence is presented to show that the hornblende in the charnockite was not due to retrograde metamorphism and the conclusion is drawn that the crystallization of hypersthene is not evidence of dry conditions of metamorphism.
The Structure of Brøggerhalvøya, Spitsbergen
Authors: Challinor A. 
Published: May 2009

AbstractBrøggerhalvøya is situated on the north-west coast of the island of Vestspitsbergen. It is shown to contain a fold and overthrust complex of Tertiary age. Large northerly movement of Pre-Cambrian rocks, previously metamorphosed in the Caledonian diastrophism, occurred over deformed but unmetamorphosed Permo-Carboniferous and Tertiary rocks on a major curved over-thrust. The structure is complicated by rapid plunge variations and subsidiary faulting. The existence of a large klippe is demonstrated and the formation of curved thrust surfaces is discussed.A brief summary of the stratigraphy is given and its important relationship to the structure discussed. A new lithostratigraphical scheme of nomenclature is proposed.
The Cambrian Lower Boundary Problem
Authors: Rozanov A. Yu. 
Published: May 2009

ABSTRACTBased on the study of distribution of assemblages of skeletal organic remains we have established the synchronous appearance of a skeleton in certain fossil groups; this enables us to draw the lower boundary of Cambrian according to the first zone with a certain assemblage of skeletal fossils.Wide distribution, in sections of various parts of the world, of deposits having no trilobites but containing similar assemblages of other skeletal fossils, has made it possible to distinguish them as an independent Tommotian stage. In Siberian sections this can be subdivided into three zones based on archaeocyathans.The deposits of the Tommotian stage are underlain by deposits containing no skeletal fossils; in their carbonate composition they are, as a rule, rich in oncolites and catagraphs (algae of uncertain affinities or products of algal activity), and stromatolites of a socalled “Vendian” or “Yudomian” assemblage.A regular distribution of assemblages of organic remains in the Cambrian-Pre-Cambrian boundary layers point to a leading role for a biostratigraphical method in the solution of the problem of the Cambrian lower boundary.
Deformation of Pebbles in Lower Old Red Sandstone Conglomerates Adjacent to the Highland Boundary Fault
Authors: Ramsay Donald M. 
Published: May 2009

AbstractThe deformation produced by the pre-Upper Old Red Sandstone movements on the Highland Boundary Fault in a zone close to the fault was sufficiently intense to rupture the pebbles in conglomerates. The patterns of pebble fracturing are similar in type and orientation over a wide area and are comparable with the patterns obtained in the experimental deformation of brittle materials. In experimental deformation a direct relationship has been established between the fractures and the causal stresses and so from a statistical orientation of the fractures in the pebbles the directions of the principal stresses can be deduced.The principal compression in the vicinity of the Highland Boundary Fault acted N.W.–S.E. varying in places to N.N.W.–S.S.E., normal to the trend of the fault, while the least principal stress acted parallel to the strike of the fault.The orientation of the least principal stress parallel to the direction of the fault in the conglomerates arises through increased stress in a vertical direction due to the nature of the downbuckling of the rocks on the southern side of the fault.The orientation of the maximum compression confirms the Highland Boundary Fault as a reverse fault of late Caledonian age rather than a Proto-Armorican wrench fault produced by N.N.E.-S.S.W. compression.
An Analysis of the Areal Distribution of Soil Size Facies on the Lower Greensand Rocks of East-Central England by the Use of Trend Surface Analysis
Authors: Chorley Richard J. 
Published: May 2009

AbstractProgressive fitting of linear, quadratic and cubic partial trend best-fit surfaces to median grain size (X1, in mm.) and percentage of silt and clay sizes (X3) of soil samples taken from fifty locations on the Lower Greensand outcrop between Ely and Leighton Buzzard in east-central England permit up to about 40 per cent of the total sums of squares to be “explained”. The successively higher levels of mathematical generalization of regional soil size distribution indicate a decrease in soil grain size towards the south-east, a disparity between the alignment of the soil facies and the strike of the present outcrop, and the existence of zone of abnormally coarse soil facies just to the west of the line of the rivel Ivel. These three features of the regional distribution of soil sizes are interesting in that they correlate with observations which have been made on the regional distribution of bedrock size facies. Finally, a suggested correlation is made between the local zones of small median grain size and abnormally high proportions of silt andclay soil sizes—isolated as “deviations or residuals” from the fitted regional surfaces—and localities where small admixtures of glacial drift (evidenced by the presence of flints) have been observed.
Strain Slip Cleavage in the Ordovician Sediments of Central Victoria
Authors: Beavis F. C. 
Published: May 2009

AbstractAt a late stage of folding, strain slip cleavage was imposed on the pelitic sediments of the Ordovician greywacke-slate association in Central Victoria. The nature of the cleavage surfaces was controlled by the type of sediment in which they were developed. In the coarser siltstones, and in the interlaminated zone of oscillatory graded beds, they are second order shear zones. In the finer siltstones and slates they are thin continuous shear domains of the first order.
The Stratigraphical Nomenclature of the Lower and Middle Jurassic Rocks of the Hebrides
Authors: Morton N. , Hudson J. D. 
Published: May 2009

AbstractThe stratigraphy of the Lower and Middle Jurassic rocks of the Hebrides is briefly summarized, and the lithostratigraphical nomenclature reviewed. To replace the inappropriate name “Inferior Oolite” for the lower marine part of the Middle Jurassic a new name, Bearreraig Sandstone Series, is proposed. This series is defined, and the succession at the type section is summarized.
Magnetic Grain Fabric Studies of the Middle Coal Measures of the Southern Part of the South Staffordshire Coalfield
Authors: Iorwerth H. ab , Hamilton N. , Loveland P. J. 
Published: May 2009

AbstractMeasurement of the anisotropy of magnetic susceptibility of Westphalian sandstones from the southern part of the South Staffordshire Coalfield shows that there is a weak preferred grain orientation. There is a significant within-sample consistency of fabric lineation and the results agree with other geological evidence. The palaeocurrent pattern is complex as may be expected within a fluvial or deltaic regime. This preliminary study suggests that this magnetic fabric technique may be used to determine the detailed palaeocurrent pattern within the Upper Carboniferous of the Midland Province.
Tertiary and Cretaceous sediments in solution pipes in the Devonian Limestone of South Devon, England
Authors: Brunsden D. , Doornkamp J. C. , Green C. P. , Jones D. K. C. 
Published: May 2009

SummaryLarge sediment-filled solution pipes in Middle Devonian Limestone near Newton Abbot are described. A succession of gravels, sands and clays is identified in the pipes, and the presence of umber, ochre and residual clays is noted. The unusually large size of the pipes is discussed and the infilling sediments are related to the Cretaceous and Tertiary formations of the nearby Bovey Basin and Haldon Hills.
Greenstone assimilation by tonalite magma, Atikwa Lake, Ontario
Authors: Heimlich R. A. 
Published: May 2009

SummaryIn the Atikwa Lake area biotite tonalite grades into a peripheral zone of hornblende tonalite as the contact with greenstone wallrock is approached. Greenstone inclusions, common within the hornblende tonalite, exhibit varying degrees of digestion and the host becomes more mafic near many such inclusions. The hornblende tonalite is more heterogeneous than the biotite tonalite, particularly near the contact with greenstone where inclusions are abundant. Modal analyses indicate the presence of large amounts of hornblende near the contact. Spectrographic analyses of composite tonalite samples show that silica decreases while alumina, iron oxide, magnesia, lime, titania, nickel, chromium, and vanadium increase toward the contact. As a whole the data support the conclusion that the peripheral hornblende tonalite is a contamination product which resulted from the assimilation of greenstone by intruding biotite tonalite magma.
Reinterpretation of the Aravalli basal conglomerate at Morchana, Udaipur district, Rajasthan, western India
Authors: Naha K. , Majumdar A. 
Published: May 2009

SummaryThe supposed Aravalli basal conglomerate near Morchana, considered to mark an erosional unconformity above the older Precambrian Banded Gneissic Complex in central Rajasthan, is a tectonic mélange in a terrain involved in superposed deformations. The supposed pebbles represent tectonic inclusions of various shapes, formed by isoclinal folding, stretching and disruption of concordant, pre- or early-kinematic vein quartz and rare pegmatite sheets in the Aravalli mica schist during the first folding.
Aeolian cross-stratification in the Devonian of the Dingle Peninsula, County Kerry, Ireland
Authors: Horne Ralph R. 
Published: May 2009

SummaryCross-stratified units, of the order of 1 to 12 m thick, are described from the Devonian Slieve Mish Group in the Dingle Peninsula of south-west Ireland. They are composed entirely of purplish-red or yellowish-grey and violet, medium- to fine-grained sandstone. An aeolian origin for this cross-stratification is indicated by the large size and morphology of the fore-sets, the excellent sorting of the sandstones and the associated evidence of aridity in a continental environment within a restricted basin.
Orford, Suffolk: Further Data on the Quaternary Evolution of the area
Authors: Carr A. P. 
Published: May 2009

SummaryBoreholes at, and seaward of, Lantern Marshes shed additional information on the Quaternary evolution of the Orford, Suffolk, area. The logs indicate:(i) a more complex surface to the London Clay, which is shown to reach depths below those formerly thought;(ii) the reality of the lower planation surface previously recorded. The surface is, however, cut across Scrobicularia and Butley (Red) Crag to a greater extent than anticipated. It proves that at least part, and probably all, of the −8.5 to −11 m surface is post Ludhamian.(iii) a peat sample from −9.4 m indicates that relative mean sea level at 7010 B.P. was at approximately −10.7 m. The peat is overlain by shingle and confirms the residual shingle structures as later than that time.
A note on an analcite-bearing lamproite from Devonshire
Authors: Velde Danielle 
Published: May 2009

SummaryThe olivine minette described by Tidmarsh from the Holmead Farm, Lox-beare, contains analcite microphenocrysts in addition to olivine, biotite, clinopyroxene and alkali-feldspar. A new chemical analysis shows that the rock is undersaturated with respect to silica. This is still another example of analcite occurring in a potash-rich rock.
Particle rounding in beach gravels
Authors: Bluck Brian J. 
Published: May 2009

SUMMARYSplitting, crushing and spalling which occur when boulders move against each other, generate fine material and so give rise to angular large and small sizes. The nature of the rounding process can be deduced from the analysis of moments of the roundness frequency distribution of the size range 4–128 mm. A low standard deviation indicates the dominance of one process—either abrasion or breakdown; a high standard deviation indicates the presence of both. The relationship between mean roundness, standard deviation of roundness, skewness of roundness and mean size allows for an analysis of the size reduction processes at work on the sediment; and for a comparison between the reactions of different rocks. A model, based on actual data, is given for the evolution of roundness of limestone clasts on a beach.
On the usage of nepheline-basalt, olivine-nephelinite, olivine-nemafite, and similar rock names
Authors: Morgan W. R. 
Published: May 2009

SUMMARYThe usage and synonymity of the names of some olivine-bearing feldspathoidal extrusive rocks is discussed. In the nephelinic rocks it is suggested that the terms nepheline-basalt and olivine-nemafite be abandoned, and that the use of olivine-nephelinite be continued. A similar recommendation is made for other feldspathoidal rocks.
Mafic hybrid rocks from the New England Batholith, New South Wales
Authors: Phillips Evan R. 
Published: May 2009

SUMMARYIntrusion of an adamellite with K-feldspar megacrysts into metadolerite wall-rock has produced a hybrid rock with K-feldspar porphyroblasts and quartz “ocelli” rimmed by hornblende. This indicates a high-level development of the feldspar and suggests that mafic contamination is an important factor in the genesis of the xenolith-rich porphyritic adamellite.
The Basal Rocks of the Tertiary at Uloa, Zululand, South Africa
Authors: Frankel J. J. 
Published: May 2009

AbstractAt Uloa in Zululand a nodule bed is the basal formation of a thin group of Tertiary sediments that rests on nearly horizontal Senonian silty mudstones. It contains mammillary, botryoidal, and cylindrical nodules, remanié Lower and Upper Cretaceous mollusca all ferruginized and partly pyritized, silicified Cretaceous wood, worn Tertiary sharks' teeth, and cetacean bone, phosphatized nodules of both Upper Cretaceous and Victoriella-bearing Eocene, and Tertiary glauconitic sandstone pebbles dated at 55 million years.A coquina-like limestone (“Pecten Bed”) overlies the irregular upper surface of the nodule bed disconformably. Consideration of some of the megafossils, the absence of larger Foraminifera, and the presence of Orbulina universa suggest that the “Pecten Bed” is Middle to Upper Miocene in age.Alternations of coarse and fine grained calcarenite layers that overlie the “Pecten Bed” disconformably, may be of youngest Miocene age.The nature of the Tertiary rocks suggests shallow water sedimentation from the Eocene to latest Miocene, with several periods of transgression and regression, and slight epeirogenic or eustatic movement only.
Metamorphosed Lamprophyres and the Late Thermal History of the Moines
Authors: Johnson M. R. W. , Dalziel I. W. D. 
Published: May 2009

AbstractCertain lamprophyres in Moidart exhibit at least three sets of minor structures (cleavages, lineations and small-scale folds). During the formation of the first set the lamprophyres acquired a schistose fabric: hornblende and biotite laths crystallized along the axial surfaces of tightly compressed folds. The deformation episodes recognized in the lamprophyre sheets post-date the main episodes of major and minor folding (F1-F3) that affected the surrounding Moine gneisses. The existence of a metamorphic fabric in these lamprophyres raises interesting problems—was the thermal energy required to “metamorphose” the lamprophyres derived from deformational heat, or by a heat flow from the Moine country rocks, or were the lamprophyres deformed during cooling and consolidation from the magmatic state (autothermal metamorphism) ?
Joints: Their Initiation and Propagation with Respect to Bedding
Authors: Hill Patrick Arthur 
Published: May 2009

AbstractJoints (fractures) are propagated from areas of high to areas of low stress. They may originate at inhomogeneities on, or by slickensiding along bedding planes. Plumose marks on the surfaces of joints radiating from volcanic, meteor, or man-made explosion craters should, in stratified rock, reveal whether the joints were propagated with their leading edge convex or concave forward.
F1 Cross-folding in the Manx Slate Series, Isle of Man
Authors: Simpson Alexander 
Published: May 2009

AbstractThe acute F1 folds in the Isle of Man possess Caledonoid axial planes and plunge predominantly to the north-eastern or south-western quarters at a low angle. Synchronous F1 cross-folding is locally developed and plunges steeply to the north-west or south-east. The axial planes of these acute structures have the same steep Caledonoid orientation as their orthodox associates and they share the same first axial-plane cleavage (S1). The generation of the cross-folding is related to original culminations and depressions in the Caledonoid hinges of the large-scale F1 folds. Comparison is made with early cross-folding in other parts of the Caledonides.
Centre-finding in Systems of Lines
Authors: Frost Michael J. 
Published: May 2009

AbstractMethods for studying the geometry of radiating and concentric features are described and compared. The method favoured for radiating features is to assume that the straight lines, which represent the trends of the features, are of infinite length. Then, for each point on a grid, calculating the mean of the perpendicular distances from the point to each of the lines. These values are then contoured, and a centre minimizing the value of the mean estimated visually.The methods are applied to finding the centre of the Lyttelton volcano from the external contours and finding a radiation centre for its radial dykes.
Chronostratigraphy and Biostratigraphy
Authors: Hedberg Hollis D. 
Published: May 2009

AbstractComments are given on a number of papers dealing with principles and procedure in stratigraphic classification which have appeared in British journals during 1963–65. It is emphasized that a clear distinction should be made between biostratigraphic units—bodies of rock strata characterized by certain palaeontological features and bounded by the limits of known occurrence of such features—and chronostratigraphic units—bodies of rock strata characterized by representing the rocks formed during certain time-spans of earth history and bounded above and below by isochronous surfaces. Biostratigraphic zones and the chronostratigraphic terms chronozone and stage are discussed.
A Spiral Brachidium in the Jurassic Chonetoid Brachiopod Cadomella
Authors: Cowen R. , Rudwick M. J. S. 
Published: May 2009

AbstractA spiral brachidium has been discovered in the Lower Jurassic brachiopod Cadomella, which is generally regarded as the last representative of the Chonetidina. Cadomella is transferred to the Koninckinidae, which are considered to be spire-bearing Chonetidina rather than aberrant Spiriferida. This interpretation implies another independent evolution of spiralia within the Brachiopoda.
Structures in the Upper Purbeck Beds at Peveril Point, Swanage, Dorset
Authors: Cosgrove M. E. , Hearn E. W. 
Published: May 2009

AbstractStructures in the Upper Purbeck Beds at Peveril Point, Swanage, Dorset, are described. Interpretation of the overall structural pattern has been attempted by constructing a three-dimensional model of the Broken Shell Limestone surface, upon which the more complex folding of the shales and marbles has taken place. The regional setting of the structures is discussed.
A Study of the Potash Felspar Gneisses of Connemara and Felspar Comparison with the Galway Granite
Authors: Leggo P. J. 
Published: May 2009

AbstractEighteen potash felspars from the potash felspar gneisses of the Connemara migmatite belt have been partially analysed and the associated plagioclase optically determined. Comparisons have been made with seventeen similar felspar pairs from the Galway Granite. Albite components are expressed graphically in an attempt to illustrate sodium distribution between associated felspar phases. On such a plot it is possible to contrast the “magmatic” felspars of the Galway Granite with those of the migmatitic gneisses; the separation of the two fields being a function of total rock chemistry. Crystallization temperatures have been determined by the two felspar method and the range 460 to 480° C. is thought to represent retrograde amphibolite conditions in the migmatitic gneisses, while petrographic evidence supports 550° C. as the temperature of amphibolite facies metamorphism in these rocks. Triclinicity measurements have also been made on the analysed potash felspars.
Initial melting in alkali feldspar-plagioclase-quartz systems
Authors: Weill Daniel F. , Kudo Albert H. 
Published: May 2009

SUMMARYThe beginning of melting of mineral assemblages of alkali feldspar, plagioclase and quartz in the system Ab-Or-Q-An cannot be treated in terms of eutectic points in subsystems which are defined on the basis of the ratio Ab/ An. Such subsystems do not exhibit unique melting temperatures or unique compositions of the first liquid produced. It is shown theoretically and demonstrated experimentally that these three minerals may coexist with liquid over a considerable portion of the melting range.
Pre-tectonic metamorphic crystallization in the Mt. Lofty Ranges, South Australia
Authors: Fleming P. D. , Offler R. 
Published: May 2009

SUMMARYEvidence for the growth of andalusite and staurolite porphyroblasts prior to the first penetrative movements in the rocks of the Mt. Lofty Ranges is presented. The implications of this unusual observation are discussed.
The Jimberlana Norite, Western Australia – a smaller analogue of the Great Dyke of Rhodesia.
Authors: Campbell I. H. , McCall G. J. H. , Tyrwhitt D. S. 
Published: May 2009

SummaryThe Jimberlana Norite Intrusion, situated near Norseman, Western Australia, is the first real analogue of the Great Dyke of Rhodesia to be discovered. The intrusion has the external form of a dyke, extends for at least 180 km (112 miles), has a maximum width of 2.5 km (1.5 miles), and follows the general easterly trend of the other members of the Widgiemooltha Dyke Suite, all of which have so far revealed characteristics of true dykes. It has a very steep funnel-shaped cross-section, like the Great Dyke, and shows many internal, canoe-shaped complexes along its length, consisting of cumulate ultramafic and basic rocks together with minor acid differentiates. The ultramafic and basic rocks display phase, rhythmic and cryptic layering. The differentiation sequence from ultrabasic to basic rocks is repeated more than once, and therehave clearly been several pulses of magma up the tensional opening. This is confirmed by the recognition of at least two magmatic unconformities. The broader petrogenetic questions posed by this unusual intrusion are discussed.
Tectonic ripples and associated minor structures in the Silurian rocks of Denbighshire, North Wales
Authors: Warren P. T. , Harrison R. K. , Wilson H. E. , Smith E. G. , Nutt M. J. C. 
Published: May 2009

SummaryStructures affecting certain bedding planes, and simulating sedimentary ripples, have been found at a number of horizons in the Wenlock and Ludlow rocks of Denbighshire, North Wales. The megascopic appearance of the ripples, including their association with linear structures and their miscroscopical fabric are described in detail; and it is concluded that they are of tectonic origin, being manifestations of bedding-plane slip. The orientations of the ripples and other minor structures suggest that the stress responsible was the regional stress that produced folding, faulting and cleavage.