bluuebunny/crossref_metadata_2025_split huggingface dataset:
Certain mechanical aspects in comparative continental rifting with a special reference to the Baikal rift
Authors: Bahat Dov 
Published: May 2009

SummaryIn the Baikal rift fracture initiation, propagation and bifurcation occurred under energy conditions considerably higher than in other continental rifts. The brittle fracture of this rift was strongly influenced by the adjacent Siberian platform. Comparative continental rifting suggests that rift initiation reflects local mantle rather than regional crustal conditions. Three aspects related to fault bifurcation in rifts include intensity and repetition of branching, as well as displacement along branching planes; the three should be distinguished.
Tretaspis radialis Lamont and allied species (Trilobita)
Authors: Price D. 
Published: May 2009

SummaryRecently discovered specimens from the Portrane Limestone Formation of eastern Ireland are regarded as topotypes of Tretaspis radialis Lament and used to further characterize the species. The features shown by these specimens confirm the close relationship between T. radialis and forms from Zones 2–4 of the Cautleyan Stage of northern England and Wales and allow its differentiation from T. moeldenensis Cave and from another related form of low Rawtheyan age which is here erected as a new species, T. caritus sp.nov.
Discovery of Late Precambrian trace fossils in Jersey, Channel Islands
Authors: Squire A. D. 
Published: May 2009

SummaryFeeding burrow trace fossils are recorded from the Upper Brioverian of St Ouen's Bay, Jersey. The traces resemble Sabellarites (Dawson) and represent deep water turbidity metazoans of Late Precambrian age, which are unknown in the remaining Brioverian of the Massif Armoricain.
The petrology of the basic and intermediate rocks of upper Swat, Pakistan
Authors: Jan M. Qasim , Kempe D. R. C. 
Published: May 2009

SummaryA series of metamorphosed (amphibolite facies) basic and intermediate igneous rocks from upper Swat, Pakistan, is described, with seven chemical analyses. The rocks intrude ?Palaeozoic metasediments and are partially bordered by other, later, intrusive and volcanic rocks. The group, now represented by, from S–N, epidote amphibolites, amphibolites, noritic and hypersthene gabbros, and quartz diorites, is considered to be derived from a series of plagioclase hypersthenites, norites, hypersthene gabbros, and hypersthene diorites. Variation diagrams are used to show that the series forms a differentiated sequence; FMA and lime-alkali diagrams suggest that it is similar to the rocks of the Garabal Hill–Loch Fyne area of Scotland. Some of the mineralogy of the group is briefly discussed, with five chemical analyses. A K/Ar age determination gives 67 Ma; thus the rocks probably derive from an early Himalayan (Alpine) tholeiitic basalt magma.
A review of the Triassic vertebrate faunas of Svalbard
Authors: Cox C. B. , Smith David G. 
Published: May 2009

SummaryIdentifications of new material collected by Cambridge expeditions and a new find from Hopen are discussed with reference to earlier work and to the stratigraphic setting. All available generic names relating to Svalbard material are listed systematically. A supplement to the alphabetical index of records (Buchanet al., 1965) is added.
Scapolite compositional change in a metamorphic gradient and its bearing on the identification of meta-evaporite sequences
Authors: Kwak T. A. P. 
Published: May 2009

SummaryScapolite occurs in the NE Mt Lofty area of South Australia in rocks of bulk compositions as diverse as sulphide-rich veins, meta dolerite, scapolite (pelitic) schists, calc-silicate rocks and impure marbles. Scapolites analysed from all these rocks show with increasing grade a linear to near-linear change in composition from Me50 and Me66. Some scatter around these values is attributed to local perturbations of fCl/fCo2 in the fluid phase during metamorphism. Sulphur values as SO3 are below the 0.02 level even when scapolite occurs in contact with sulphides in a vein in a small copper mine; here, however, an interpreted FeO value of 2.58 weight % was recorded. The values in this study are comparable with those of Heitanen (1967), and are believed to be representative of products of normal metamorphic fluids evolved from non-evaporitic metamorphic rocks under a greenschist–amphibolite facies gradient; they can thus be used as a standard in assessing the possible significance of meta-evaporites in other areas.
The Ashgill Series near Welshpool, North Wales
Authors: Cave R. , Price D. 
Published: May 2009

SummaryThe name Trawscoed Mudstone Formation is proposed for previously undescribed mudstones cropping-out between the Caradoc Nod Glas Formation (‘Gwern-y-Brain Group’ of Wade, 1911) and the overstepping Rhuddanian Powis Castle Conglomerate Formation some 5 km NW of Welshpool, North Wales. The mudstones have a fauna, dominated by brachiopods and trilobites, which indicates that they are contained within the Cautleyan Stage of the Ashgill Series and suggests deposition in a deep shelf environment.
Layered gabbros in the Eastern Lizard, Cornwall, and their significance
Authors: Kirby G. A. 
Published: May 2009

SummarySmall-scale igneous layering and lamination have been found in the gabbro of the Eastern Lizard, Cornwall. An origin by gravitational settling of plagioclase and olivine crystals is proposed. Several post accumulation factors have obscured the lateral continuity of these features.Their present orientation suggests that the gabbro has been rotated through approximately 90° about an E—W axis and‘ tops’ to the N. This invalidates the idea of an in-situ ring intrusion but is in keeping with the ophiolite model for the Eastern Lizard.
Clastic dykes in the Namurian shales of Co. Leitrim, Republic of Ireland
Authors: Brandon A. 
Published: May 2009

SummaryA description is given of the numerous thin dolomitic sandstone dykes cutting dark marine shales of E1a age in Co. Leitrim. They are almost wholly confined to the Dough–Thur Mountain area, which is cut by the Caledonoid trending Ox Mountain and Belhavel Faults. It is thought probable that movement along one of these faults, possible in E1c times, conferred thixotropic properties to a sand horizon in the marine shales and also produced fractures in the shales up which the sand was intruded.
Contributions to the Neogene radiometric time-scale from northern Africa
Authors: Vass D. , Badgasarjan G. P. , Bajanik S. 
Published: May 2009

SummaryFour volcanic rocks from northern Tunisia and a syntectonic granite from northeastern Algeria were dated by the K—Ar method. The stratigraphic position of the dated rocks is determined mainly by their relationship to biostratigraphically calibrated Miocene tectonism. The K—Ar age of the granite, which is younger than latest Burdigalian and older than Early Tortonian, is 16.8 m.y. (*15.8 m.y. calculated with western decay constants). Rhyodacite at 10.9 (*10.4), rhyolite at 8.8 (*8.3), basalt at 7.3 (*6.9) and adesite at 7.0 (*6.7) m.y. are all apparently younger than Lower Tortonian.
A bedded deposit of anthophyllite schist in the Precambrian belt of Nellore, South India
Authors: Rao T. Ramamohana 
Published: May 2009

SummaryA pure anthophyllite schist occurs as a bedded deposit conformable with garnet-bearing quartz—muscovite, and quartz—chlorite—biotite schists and diopside-bearing caic-silicate rocks in the north-central part of the Nellore Schist Belt. Field and petrochemical studies show that anthophyllite schist has formed from regional metamorphism of Fe-, Mg-rich aluminous sediments aided by metamorphic differentiation due to local kinematic action under amphibolite facies conditions which is the general grade of metamorphism of the Nellore Schist Belt. A pure anthophyllite schist of sedimentary origin reported here is the first of its kind described from any terrain.
The geology of the Vesturhorn Intrusion, SE Iceland
Authors: Roobol M. J. 
Published: May 2009

SummaryThe Vesturhorn Intrusion, exposed over 19 km2 of the south-eastern coast of Iceland, comprises two mafic complexes and a central core of epigranites. The latter can be subdivided into a central area with a flat-lying sheet structure, surrounded and separated from the mafic complexes by a more massive belt called the Transitional Epigranites with variable colour index and containing many rounded-to-angular inclusions and net-veined complexes. The consideration of several lines of evidence suggests that the components were emplaced as magmas in the sequence, first the epigranites with a sheet structure and second the basic complexes. The Transitional Epigranites appear to have originated by the remobilization and local hybridization of the early, sheet-structured epigranites. The relatively large volume of remobilized material and an absence of partially melted zones are considered to result from the early epigranites being still partially molten at the time of emplacement of the mafic complexes, together with a ponding of remobilized material beneath the chamber roof. A final intrusive episode occurred with the emplacement of a body of fayalite—hedenbergite epigranite largely into the Transitional Epigranites, probably after the consolidation of the latter.
Foraminiferid-encrusted ooids: evidence for ancient subtidal algal mats?
Authors: Talbot M. R. 
Published: May 2009

SummaryOoids and grapestones from some parts of the Corallian Beds (Oxfordian) contain encrustations of the foraminiferid Nubeculinella. Encrusted layers within ooids clearly reveal lengthy periods when the grains were stationary and not accreting carbonate laminae. It seems likely that during colonisation by the foraminiferids the ooids were immobilised beneath a subtidal algal mat and there are indications that the mats were sufficiently coherent to bind lumps of sediment together during disruption by burrowing organisms.
Evolution of Nigeria's Benue Trough (Aulacogen): a tectonic model
Authors: Olade M. A. 
Published: May 2009

SummaryThe tectonic evolution of Nigeria's Benue Trough has recently been the focus of investigations, especially in relation to continental drift and opening of the South Atlantic Ocean during Cretaceous times. Most of the tectonic models presented for the Benue depression have placed undue emphasis on certain plate tectonic concepts which are inconsistent with the salient geologic features of the trough. A possible model, involving the rise and cessation of mantle upwelling beneath a Cretaceous hot spot, and attendant patterns of doming, rifting, sedimentation, magmatism and tectonism, is proposed for the Benue aulacogen.
Tholeiite from the Cenozoic alkaline volcanic province of Nigeria
Authors: Wright J. B. 
Published: May 2009

SummaryBouldery outcrops of coarse-grained olivine-free lava, containing abundant orthopyroxene and clinopyroxene, mostly in glomerophyric aggregates, occur over a small area among the Tertiary to Recent volcanics of the Jos Plateau, Nigeria. This is the only rock of tholeiitic affinity in an otherwise completely alkaline volcanic province. Petrographically it does not greatly resemble tholeiitic occurrences reported from such provinces elsewhere, but that is believed to be due more to a relatively complex crystallization history than to any fundamentally different process of magma generation. It is not regarded as representing a tholeiitic parent for the alkaline lavas of the Jos Plateau region.
Some curious garnet clusters from the Garnetiferous Beds of the Leinster Granite Aureole
Authors: Kennan P. S. 
Published: May 2009

SummaryHollow, often ellipsoidal, clusters of small manganiferous garnets are described. They occur as discrete entities in the normal garnet–quartz coticule fabric of the Garnetiferous Beds, an important group of metamorphosed manganese-rich sediments found within the aureole of the Leinster Granite. The clusters are thought to represent small original sedimentary concretions, subsequently completely reconstituted.
The Indus Suture Line, the Himalaya, Tibet and Gondwanaland
Authors: Crawford A. R. 
Published: May 2009

SummaryMisunderstanding exists about the origin of the Himalaya, Indo-Tibetan relationships and the extent and history of Gondwanaland. The Indus Suture Line is a relic of fracture to the mantle but for a period only represented by the faunas of the ‘exotic blocks’ of the Tibetan Himalaya, i.e. Permian—Late Jurassic. Tibet appears originally to have been part of a plate including India, but submerged while India remained continental. Associated with the fracture extending to the mantle represented now by the Indus Suture Line, shallower subparallel fractures developed within which the Gondwana sediments of the Himalaya were preserved. These, together with the salt at the base of the Tethyan marine sequence, facilitated intra-continental orogeny when, much later, India was affected by vigorous sea-floor spreading and plate movement in the NW Indian ocean after it had become attached to Asia.The northern plate boundary was beyond Tibet, on the N side of the Tarim Basin Block, and along the Tien Shan. The Tien Shan present peculiar features, particularly very deep long intramontane depressions such as Issyk Kul in USSR and Turfan-Hami in China, and their stratigraphy shows persistent mobility. The Tarim Basin Block has moved sinistrally relative to Tibet and in Gondwanaland lay near northern Western Australia. The suggested extent of Gondwanaland explains the present lack of continental crust W of Western Australia, now in Tibet, and the intracontinental origin of the Himalaya is consistent with the absence of recent volcanism in an area of considerable seismicity. The association of Tibet with India in Gondwanaland destroys the effectiveness of arguments against continental drift based upon the extension of Indian stratigraphic sequences across the Himalaya. The hypothesis of an enlarged Gondwanaland is given support by recent Chinese discoveries of terrestrial vertebrate fossils of Gondwanic type near the Tien Shan.
The Shell of Devonian Atrypida (Brachiopoda)
Authors: Copper Paul 
Published: May 2009

AbstractA simple visual method for distinguishing important Devonian atrypid brachiopod taxa, and for separating the Atrypidae and Palaferellidae family-groups is outlined. The thickness, distribution, and repetition of the three layers of impunctate atrypid shell wall differ markedly from one genus to the next and show a general evolutionary trend towards reduction and simplification.
A Review of Wenlock and Ludlow Stratigraphy and Sedimentation in N. W. England
Authors: Furness R. R. , Llewellyn P. G. , Norman T. N. , Rickards R. B. 
Published: May 2009

AbstractRecent studies in N.W. England have indicated the need for a review of Wenlock and Ludlow (Silurian) stratigraphy. Detailed re-mapping, mainly for the first time since 1872, has modified and more clearly defined the established terminology. Determinations of new graptolite and shelly faunas have resulted in a revision of some earlier work and the establishment of a modern zonal classification for parts of the Wenlock and Ludlow. Lithofacies are broadly summarized and described with comments on some palaeocurrent data.
Seismically-induced load structures in the basal Coal Measures, South Wales
Authors: Weaver J. D. 
Published: May 2009

SummaryWithin the basal Coal Measures between Ystradgynlais and Abercraf a number of liquefaction layers are seen displaying ball and pillow structures. These layers consist of balled-up, ovoid masses of sandstone some 0.25–0.3 m thick and 0.5–0.7 m across. It is considered that they were formed by loading, resulting from the lique-faction of underlying silts, produced by the passage of earthquake shock waves associated with the main fault zone of the Swansea Valley Disturbance. Elsewhere in South Wales, horizons displaying load and slump structures in rocks of Upper Palaeozoic age may have resulted from seismic shock waves caused by contemporary movements along major Variscan fractures.
The 1973 Heimaey Strombolian Scoria deposit, Iceland
Authors: Self S. , Sparks R. S. J. , Booth B. , Walker G. P. L. 
Published: May 2009

SummaryThe 1973 eruption on Heimaey, Iceland, presented the opportunity to study the interaction of the principal factors that control the formation of pyroclastic fall deposits. The grain size characteristics and the dispersal of some of the scoria fall units within the Eldfell Scoria deposit are described and related to observations made on the wind speed and direction, the height of the eruption column, the ‘muzzle’ velocity and the various styles of activity during the first month of the eruption.
A re-evaluation of the blueschist facies
Authors: Wood R. M. 
Published: May 2009

SummaryThe blueschist facies metamorphism has always been one of the most difficult to quantify. This is for two important reasons. Firstly, the temperatures and pressures of the facies tend to be inaccessible to experimental analogues of the blueschist indicator minerals: aragonite, glaucophane, jadeite and lawsonite. Secondly, the conditions of blueschist metamorphism are not typical of the earth's crust. For a rock to be metamorphosed under lower temperatures at a given pressure than those of normal geothermal gradients (considered here as negative deviation metamorphism) requires ‘rapid’ downwarping and reuplifting. The movement during metamorphism, combined with hydration rather than dehydration (a feature of this environment) fails to preserve a single metamorphic culmination and hence the mineralogy and textures of blueschist assemblages may fail to match the conventional phase equilibrium metamorphic model. Thus the simple phase equilibrium interpretative basis of metamorphic petrology is recognized as only a special case of a more general theory of metamorphic chemical/mineral interaction.
Glaucophane Schists of Caledonian age from Spitsbergen
Authors: Horsfield W. T. 
Published: May 2009

SummaryGlaucophane schists from Oscar II Land in western Spitsbergen are described for the first time. Although lawsonite, aragonite and pumpellyite have not been found, the mineral assemblages correspond generally with glaucophane schist assemblages known from elsewhere. The results of three XRF chemical analyses are presented, and five K/Ar radiometric determinations. The radiometric dating and field evidence both suggest that the glaucophane schists are a result not of the Tertiary orogeny which affected this part of Spitsbergen, but of the earlier Caledonian orogeny.
Microfabrics of a recumbent fold in cross-bedded sandstones
Authors: Yagishita K. , Morris R. C. 
Published: May 2009

SummaryA thin-section study of the orientation of long-axes of quartz grains was conducted for a similar type fold of overturned cross-bedding in Carboniferous sandstones. Preferred orientation of detrital grains of the fold shows that (a) apparent long-axes of grains are parallel to the axial plane in a plane normal to the fold axis, (b) long-axes of grains in the axial plane are oriented in a high angle to the fold axis, and (c) grains are aligned parallel to the fold axis in a plane perpendicular to the other two directions. From the dimensional orientation of quartz grains in this sample, it is concluded that the overturned fold was made by a shear mechanism immediately following sedimentation in which the original quartz grains were reorientated by small-scale slippage along the shear planes.
Post-cumulus disruption of the Lilloise Intrusion, East Greenland
Authors: Matthews D. W. 
Published: May 2009

SummaryField, petrographic and chemical evidence from the cumulates of western Lilloise suggest a substantially higher level of exposure in the cumulus pile than is seen on the E side, due to relative subsistence of the western half of the intrusion. It is suggested that the subsistence started while both cumulus pile and the surrounding basalts were still hot and not fully consolidated. When, later, reactivation occurred, the rocks were in a more cohesive state and ‘syenitic’ magma was available for intrusion as discrete sheets and veins.
The petrology and geochemistry of the Creag Dubh composite sill, Whiting Bay, Arran, Scotland
Authors: Rogers N. W. , Gibson I. L. 
Published: May 2009

SummaryAnalysis of 17 samples for both major and trace elements reveals that, unlike most other Tertiary composite intrusions, the Creag Dubh sheet possesses silicic margins and a doleritic centre. The two rock types grade together rapidly without chilling at the upper and lower internal contacts. However, there is evidence for mixing of the two magma types prior to or during emplacement with the production of limited amounts of intermediate hybrids. The central dolerite appears to be later than the marginal felsites which in places back-vein the dolerite. The sequence of intrusion is tentatively related to the upward draining of a strongly zoned magma chamber.
Submarine volcanic and associated sedimentary rocks of the Fuerteventura Basal Complex, Canary Islands
Authors: Robertson A. H. F. , Stillman C. J. 
Published: May 2009

SummaryOn Fuerteventura, inner Canary Islands, a phase of early Cretaceous deposition on a passive continental margin was terminated in Albian time by strong localized uplift associated with onset of calcareous pelagic sedimentation. Later, during early Tertiary times, spasmodic episodes of submarine alkali volcanism led to the construction of a thick lava pile. After folding of the lower submarine volcanic rocks, and the underlying pre-volcanic sedimentary rocks, parts of the Basal Complex were emergent by Oligocene to Miocene times, fringed by coral and algal reefs. With renewed early Miocene uplift, the reefs disintegrated, followed by block faulting, intrusion of plutons, and a final phase of submarine dyke intrusion. There was then strong uplift coupled with deep erosion, extrusion of sub-horizontal Neogene plateau lavas and further intrusion of plutons. Regional comparisons suggest that tectonic events on Fuerteventura may have a bearing on sedimentary hiatuses and gravity sliding events which affected the adjacent West African continental margin.
Coccolith-rich marker bands in the English Kimmeridge Clay
Authors: Gallois R. W. , Medd A. W. 
Published: May 2009

SummaryThin coccolith-rich bands, in which coccoliths make up a major part of the rock, have been recorded at 11 horizons in the Kimmeridge Clay of Yorkshire, Lincolnshire, Norfolk, Surrey and Wiltshire and also in cliff sections at and adjacent to Kimmeridge Bay, Dorset. It seems likely that at least nine of these bands form persistent markers throughout southern and eastern England. The coccolithophorid assemblages are discussed and some species of Stradnerlithus are systematically described.
Tektites probably wholly terrestrial and related to continental movement
Authors: Crawford A. R. 
Published: May 2009

SummaryThe four groups of tektites are now widely regarded as the product of splash from a meteoritic or cometary impact melt of terrestrial rock. They include two groups (Moldavites and Ivory Coast tektites) attributed to the Nordlinger Ries and Bosumtwi craters. These craters seem unlikely to be of impact origin, though hyper-explosive. Tektites are, therefore, more probably all wholly terrestrial. For much the largest group, those of the combined Southeast Asian-Australian strewnfield, no satisfactory source is known. An origin in Southeast Asia, even by impact, is improbable. A possible source lies in Central Asia. The hyper-explosive activity is regarded as an extreme form of volcanism, a consequence locally and rarely of the continual combined vertical and ‘horizontal’ movements of continents, here termedtribulation.