bluuebunny/crossref_metadata_2025_split huggingface dataset:
A note on the age and pyroxene chemistry of the igneous rocks of the Shelve Inlier, Welsh Borderland
Authors: Lynas B. D. T. , Rundle C. C. , Sanderson R. W. 
Published: May 2009

AbstractGeological survey, electron microprobe analyses of clinopyroxenes and isotopic age determinations have revealed that the intrusive dolerites and basic–intermediate lavas of the Shelve Ordovician Inlier are part of a co-magmatic suite which show transitional affinities between tholeiites and alkali basalts. The ages of most of the intrusives are shown to be mid-Ordovician.
Structure and eruptive mechanisms at Surtsey Volcano, Iceland
Authors: Moore James G. 
Published: May 2009

AbstractGlassy basalt tuff was the primary material cored in 1979 from a 181 m deep drill hole on the east tuff ring of Surtsey volcano. Despite the fact that the hole extends 122 m below sea level all the core is similar to the exposed tephra composing the two tuff rings of the island. The tuff includes abundant accretionary lapilli and tuff vesicles, indicating that it was all deposited subaerially. During the growth of the tuff rings, repeated hydromagmatic explosion cycles began with a series of intermittent tephra-finger explosions leading up to continuous uprush explosions which lasted for several minutes to several hours. This nozzle-like continuous activity produced eruption columns 100–250 m in diameter and 500–2000 m in height which probably quarried several hundred metres below the ground surface. The continuous-uprush explosion type provides a reasonable mechanism to excavate a diatreme from the top down. During construction of the tuff rings, concentric faults repeatedly downdropped a funnel-like structure (400–800 m in diameter) several hundred metres, thus accounting for the presence of subaerially deposited tephra in the drill core far beneath sea level. Ring dykes later intruded upward along these faults and fed small lava flows. Heat in the surface tephra probably originated primarily from these shallow intrusions.
Form and mode of life of Dicellograptus (Graptolithina)
Authors: Henry Williams S. 
Published: May 2009

SummaryThe majority of Dicellograptus species have stipes which spiralled to a greater or lesser extent; this explains continuous variation of axial angle found in several species and many anomalous features of flattened or partially flattened specimens. The effects of variation in thecal style along the stipe are distinguished from those produced by variable orientation of the rhabdosome during flattening and by later tectonic distortion. It is concluded that Dicellograptus probably lived with stipes pointing upward and that the rhabdosome rotated in a horizontal plane due to eddies created by the non-directional ciliary activity of radially dispersed zooids in order to improve feeding efficiency.
Evolution and classification of some Ordovician Calymenina (Trilobita)
Authors: Henry J.-L. 
Published: May 2009

SummaryThe classification of the generaPlaesiacomiaHawle & Corda, 1847,KerfornellaHenry, 1976,ColpocorypheNovák in Perner, 1918,SalterocorypheHammann, 1977 andNeseuretusHicks, 1873, is discussed.PlaesiacomiaandKerfornellaare attributed to the Homalonotidae (sub family Kerfornellinae nov.), whileColpocoryphe, Salterocoryphe, andNeseuretusare regarded as belonging to the Calymenidae. The author's opinion is mainly based on the morphology and evolution of the coaptative devices, and on the morphology of the hypostoma.
Secondary faulting, a consequence of a single continuous bifurcation process
Authors: Bahat Dov 
Published: May 2009

SummaryFracture propagation in the crust under post-critical conditions (rapid propagation), and possibly in some instances even under sub-critical conditions (slow propagation) can produce fracture-branching in a single continuous process. Later local or regional stresses result in displacements along the fractures and secondary faulting develops. This concept can explain various secondary features like conditions of branching, branching-angle and shallow secondary faults. The splaying of the Hope Fault in New Zealand is primarily a result of early fracture bifurcation and later minor displacements.
How should igneous rocks be grouped?
Authors: Rock N. M. S. 
Published: May 2009

SummaryDespite their importance and frequency of usage, ‘grouping terms’ in petrology such as Association, Family, Lineage, Province, Series and Suite appear to lack established meanings. Partly by analogy with the recently standardized stratigraphic nomenclature, hierarchies of such terms are suggested to cover petrographic classification (rock-names), petrological classification (rock-names extended to magma-types), geographic classification (igneous provinces) and tectono-genetic classification (rock assemblages characteristic of particular tectonic regimes). Used in this way, the exact implications of each term become clearer. Again by analogy with stratigraphy, ‘Super-’ and ‘Sub-’ groupings are suggested in a few cases: ‘Subprovince’ for example can differentiate distinct rock assemblages related to separate parent magmas within one well-defined Province (e.g. nephelinite-carbonatite and basalt-trachyte assemblages in the East African Rift), and ‘Superprovince’ can be used to group coeval Provinces now separated by opened oceans, etc. (e.g. Thulean Superprovince composed of Hebridean, East Greenland, etc., Provinces). The term ‘Province’ itself carries several ambiguities; it is best confined to cases where the ages of the spatially associated igneous rocks fall within a narrow range (e.g. Oslo Province); ‘Belt’ is suggested for those where the age-range is more substantial (e.g. Jurassic-Tertiary magmatism of Southeast Brazil).
Variation of metamorphic grade in Lower Strathspey
Authors: Winchester J. A. 
Published: May 2009

SummaryThe mineral assemblages in calc-silicates collected from Ballindalloch and Bridge of Avon suggest that the grade of metamorphism is lower than in the areas to the E and W. Mild post-metamorphic warping may be responsible for the production of an apparent ‘thermal anticline’ in the Monadhliath Mountains and the complementary ‘thermal syncline’ in Lower Strathspey.
The Devonian System in China
Authors: Shih-Pu Yang , Kiang P'an , Hung-Fei Hou 
Published: May 2009

SummaryThe Devonian System of China occurs in the Tianshan–Hingan* Geosyncline of North China, the Yangtze Paraplatform of South China and in the geosynclinal areas of West China. Devonian formations are entirely absent from the Sino-Korean Paraplatform and the Tarim Platform, but along the border of the Tarim Basin and the slopes of Qilianshan (Chilienshan) are continental sequences rich in vertebrate and plant fossils. On the basis of differences in biostratigraphic characteristics the Devonian is divisible into 8 regions: 1. Junggar–Hingan (Dzungar–Khingan), 2. South Tianshan (South Tienshan), 3. Qilianshan (Chilienshan), 4. Longmenshan (Lungmenshan), 5. South China, 6. South-eastern China, 7. West Sichuan–North Xizang (West Szechuan-North Tibet), 8. Himalaya–West Yunnan.Using both lithology and fossil content, five principal facies (types) may be further differentiated: 1. Hingan type (eugeosynclinal facies), 2. Baoxin type (miogeosynclinal facies), 3. Xiangzhou type (platform near-shore facies), 4. Nandan type (platformal off-shore facies), 5. Cuifengshan (Chuifeng shan) type (continental facies).The Devonian of South China occurs in various facies, but has a well-defined principal stratotype. It has been divided by Chinese geologists into eight stages, two in the Upper Devonian, two in the Middle Devonian and four in the Lower Devonian.The Devonian sequences of the geosynclinal regions of West China are characterized by facies which contain graptolites and tentaculites, and have largely been affected by regional metamorphism. The Devonian biota of the Junggar–Hingan Region is essentially an endemic one, but it is associated with a few European and North American elements. Marine pyroclastics are the principal rocks. General stratigraphical columns of those regions are given with a correlation with other parts of China. The continental Devonian of China is unique especially in the light of its vertebrate content. Red sandstones are widespread in the Lower Devonian, and intercalated with argillaceous limestone and mudstone. This sequence is rich in endemic East Asiatic faunal elements including agnatha (Galeaspida, Polybranchiaspida), Antiarchi, etc. Middle and Upper Devonian lithostratigraphic units consist principally of light coloured quartzose sandstone formations in Southeastern China, with some red beds in South and North China, while their fauna and flora are cosmopolitan in character. Their exact geological ages vary, however, as clearly shown in the South China region, especially towards the top of the Upper Devonian (with Asterolepis) and in the early Middle Devonian (with Bothriolepis).
Displacement of sand grains in sandy gypsum crystals
Authors: Shearman D. J. 
Published: May 2009

SummarySand grains enclosed in gypsum crystals which grew in otherwise uncemented sand commonly, either float in the gypsum, or, are arrayed in sand-bearing and sand-free zones in a manner which indicates that they were displaced during growth of the gypsum. Corroborative evidence of displacement of included sand grains is found in some sandy gypsum crystals from coastal sabkhas in Abu Dhabi, U.A.E. In these crystals, dust particles which formerly coated the sand grains are strung out as festoons behind the grains and thus record the directions and extent of the displacement. The direction of displacement was outwards, normal to the traces of what had been former crystal faces. The displacement also involved some pivoting of elongate grains which now lie with their long axes in the direction of movement.
The structure and shape of the Jimberlana Intrusion, Western Australia, as indicated by an investigation of the Bronzite Complex
Authors: McClay K. R. , Campbell I. H. 
Published: May 2009

SummaryThe structure of the partly exposed lower section of the Jimberlana Intrusion has been determined by combining the geophysical evidence with the available geological and diamond drill hole data. The results have been added to the wellknown upper section to show that Jimberlana is not a dyke-like body as had previously been thought, but is a horizontal pipe-like intrusion 180 km long, 2.5km wide and 5.5 km deep, with a V-shaped cross-section. A marginal series with ‘reversed’ fractionation and high primary dips, similar to the marginal series of the Muskox Intrusion, occupies the lower part of the intrusion. The rocks of this series display rhythmic layering and a variety of cumulate textural types indicating that cumulate processes can take place during deposition on near-vertical dipping surfaces.
Vermiforichnus borings from the Ordovician of central Wales
Authors: Pickerill R. K. 
Published: May 2009

SummaryThe epizoan Vermiforichnus Cameron (1969b) from the Upper Ordovician (Caradoc) of the Berwyn Hills and the Welsh Borders is host-specific, occurring in association with the strophomenid Macrocoelia and the orthid Heterorthis. The spionid polychaete probably responsible for the production of the Vermiforichnus borings inhabited both live and dead individuals. In live individuals Vermiforichnus was located at the anterior margin and oriented perpendicular to the commissure, this position affording both a means of protection and a more efficient feeding position. In dead individuals population density was lower and the borings were randomly oriented. Vermiforichnus was restricted to inner—outer sublittoral environments and, as such, is a useful palaeoenvironmental guide.
Carbonate ball and pillow structures
Authors: Weaver J. D. , Jeffcoat R. E. 
Published: May 2009

SummaryA liquefaction layer displaying ball and pillow structures occurs within the back reef facies of the Cawdor Limestone (P2 zone) near Wirksworth. This layer consists of pillow-shaped masses of coarse biosparite within a biomicrite matrix. The pillows are 0.6–0.8 m thick and 1.5–4.0 m across. Experiments using layers of calcareous sand above calcareous mud have demonstrated that such structures may be produced by subjecting saturated sediments to seismic shocks. These Viséan carbonate ball and pillow structures are attributed to loading, resulting from liquefaction of underlying calcareous mud during the passage of earthquake shock waves associated with the Gulf Fault.
Silurian trilobites from NE Queensland and the classification of effaced trilobites
Authors: Lane P. D. , Thomas A. T. 
Published: May 2009

SummaryA trilobite fauna of Llandovery/Wenlock age is described. Five species are represented:Rhax polllnctrixgen. et sp. nov. (Scutelluidae), a warburgelline?,Sphaerexochussp.,Encrinurus?sp., and a calymenid. The morphology ofR. pollinctrixsupports the view thatBumastusis a scutelluid, and consequently that the Illaenidae, as presently conceived, is polyphyletic.
An ultramafic rock in the precambrian of eastern Sinai
Authors: Beyth M. , Grunhagen H. , Zilberfarb A. 
Published: May 2009

SummaryTwo small outcrops of harzburgite and asbestos-bearing serpentinite, occurring S of Di Zahav in eastern Sinai are the first record of ultramafic rocks from the Sinai Precambrian massif.
Oligocene alkaline igneous activity in NE Mexico
Authors: Bloomfield K. , Cepeda-Davila L. 
Published: May 2009

SummaryPotassium-argon age determinations on rocks from the Sierra de San Carlos, State of Tamaulipas, México, which are petrographically very similar to other bodies in north-eastern México and the south-central U.S.A., indicate that a NW-trending zone of alkaline complexes, at least 1,400 km in length, stretches from the Gulf coast to southern New Mexico. This zone may be structurally related to the parallel, but somewhat younger, Rio Grande rift.
The control of the whole-rock content of CaO and Al2O3 on the occurrence of the aluminium silicate polymorphs in amphibolite facies pelites
Authors: Winchester J. A. 
Published: May 2009

SummaryThe contents of CaO and Al2O3 in pelites from areas subjected to amphibolite facies metamorphism have been plotted in order to discover the compositional limit of the stability field of the aluminium silicate minerals. Rocks containing kyanite or sillimanite fall within a well-defined field, while rocks plotting outside this field are devoid of aluminium silicate minerals, irrespective of metamorphic grade. With the trace of the curve bounding this field known, the position of the kyanite isograd may be more easily plotted in areas where kyanite or sillimanite are rare.
Some migmatite types and their origins, from the Barousse Massif, Central Pyrenees
Authors: Harris N. B. W. 
Published: May 2009

SummaryObservations on the structure, fabrics, mineral assemblages and distributions of plagioclase compositions from migmatites of the Barousse Massif, Central Pyrenees, are related to the mode of differentiation of leucosome from melanosome. It is concluded that the majority of these migmatites have formed from recrystallization of sedimentary horizons, often accompanied by metamorphic differentiation, although some migmatites appear to have formed from anatexis or magmatic injection.
Three-dimensional isograds from the Lukmanier Pass, Switzerland, and their tectonic significance
Authors: Fox J. S. 
Published: May 2009

SummaryFour mineralogical zones, corresponding to the following ‘maximum’ metapelitic assemblageszone 1: chloritoid-chlorite-kyanitezone 2: staurolite-chloritoid-chlorite-kyanitezone 3: biotite-staurolite-chloritoid-chlorite-kyanitezone 4: biotite-staurolite-garnet-chlorite-kyanitehave been mapped in the Ultrahelvetic rocks of the Lukmanier area in Switzerland. Petrographic study suggests that, despite the ubiquity of ‘disequilibrium’, the zone boundaries accord with the simple univariant equilibriachloritoid+kyanite = staurolite+chlorite+quartz+H2Ochloritoid+chlorite+muscovite = staurolite+biotite+quartz+H2Oand chloritoid+muscovite+quartz = staurolite+garnet+biotite+H26Using structural contours, minimum isogradic dips of 35° north have been obtained.The Lukmanier parageneses require the Lepontine phase of Alpine metamorphism to have had a geotherma! gradient distinct from both Alpine blueschists and the Bergell contact metamorphites. The high minimum value for isograd and isotherm orientation here points to a convective heat source for the Lepontine event.
Monticules in a Jurassic Cyclostomatous Bryozoan
Authors: Taylor P. D. 
Published: May 2009

SummaryStructures similar to the monticules of Palaeozoic trepostomatous Bryozoa which occur in the Jurassic cyclostome Reptomultisparsa incrustans are described. They are interpreted as having a function analogous to that inferred for monticules. A smaller proportion of zooecia open on the monticules than between them, and, of these a higher proportion are occluded.These observations lend support to the theory proposed by Banta, McKinney & Zimmer (1974) that monticules functioned as regions of exhalant current chimneys on the zoarial surfaces of Bryozoa.
Mineralogy of Precambrian Gneiss from the Bighorn Mountains, Wyoming
Authors: Heimlich R. A. , Nelson G. C. , Malcuit R. J. 
Published: May 2009

SummaryPrecambrian rocks throughout most of the southern part of the Bighorn Mountains, Wyoming, are dominated by a biotite-bearing plagioclase–quartz gneiss containing hornblende-rich or microcline-rich layers locally. Compositional and/or optical data are presented for plagioclase, biotite, and hornblende as well as optical and X-ray data for microcline and preliminary morphologic data for zircon in the gneiss. These data, supplemented by field and petrographic observations, suggest that the gneiss was formed under conditions of the low amphibolite facies, that late-occurring potash metasomatism accompanied the metamorphism, and that the gneiss was derived from a relatively chemically uniform parent rock.
Evolution of the granulites and sub-division of the granulite facies in Ceylon
Authors: Hapuarachchi D. J. A. C. 
Published: May 2009

SummaryThree subfacies of the granulite facies are recognized: garnet–diopside–quartz subfacies; pyroxene–granulite subfacies; and hornblende–granulite subfacies The erection of a garnet–diopside–quartz subfacies follows De Waard's suggestion (1965) of a garnet–clinopyroxene subfacies. Two major divisions of the hornblende–granulite subfacies are now recognized, (i) garnet–biotite division, (ii) cordierite division. Three sub-divisions of the former are suggested on the basis of critical basic assemblages. Since wollastonite has been found to have a limited areal occurrence within the latter, a two-fold sub-division of the cordierite division is suggested on the basis of the assemblages, (a) calcite–quartz, (b) wollastonite. A seven-fold sub-division of the granulite facies is thus proposed for Ceylon rocks. An attempt is made to trace briefly the major events in the metamorphic history of the rocks supported by available geochronological evidence.
Late Pleistocene chronology and the glacial–interglacial cycle
Authors: Evans P. 
Published: May 2009

SummaryAlternative time-scales differing by 25% have been proposed for the climatic sequence revealed by deep-sea cores. Both scales are based on radiometric data. Recent evidence which is here summarized favours the time-scale which gives the smaller values for the ages of late Pleistocene events; it supports the estimate of 40 ka rather than 50 ka for the average length of the principal climatic cycle.
The Greenland O18 curve: time scale and ice accumulation
Authors: Mörner N.-A. 
Published: May 2009

SummaryNone of the time scales hitherto applied to the Greenland O18 curve is considered reliable. The logarithmic time scales were based on the false assumption of constant glacial dynamics. The latest time scale, based on a supposed constant 2400- years cycle, seems to be based on another false assumption of constant cycles. A chronology based on indirect dating therefore seems superior.
The Analysis of Core Samples and a Sparker Profile from The Wash, England
Authors: Dingle R. V. 
Published: May 2009

AbstractA microfaunal analysis of four Mesozoic core samples from The Wash is discussed, together with an interpretation of a continuous reflection profile. The profile demonstrates an expanded Lower Cretaceous succession compared with Norfolk and Lincolnshire and the clay facies of the Valanginian Hundleby Clay is shown to extend at least to the middle of The Wash. The other core samples are proved to be of Kimmeridgian, Barremian and Upper Albian age. Two Chalk samples are also plotted.
The Variation of Some Trace Elements in the Rosses Granite Complex, Donegal
Authors: Hall A. 
Published: May 2009

AbstractThe distribution of Ba, Mn, Nb, Rb, Sr and Zr has been studied in the granites of the Rosses complex. Their variation is interpreted in terms of a process of magmatic evolution involving the formation of granite magma by progressive partial fusion, and its modification during emplacement by the partial assimilation of displaced country rocks. Several greisens from the Rosses complex have also been analysed, and the changes in concentration of trace elements during greisenization are related to observed changes in mineralogy.
Geochronology of the Tristan da Cunha Group of Islands
Authors: Gass I. G. 
Published: May 2009

AbstractA geological synopsis of the three main islands of the Tristan da Cunha group is given and their rate of growth by volcanic processes, and their subsequent erosion, are examined in the light of recent radiometric age data. These data, though few as yet, suggest that each island has a “life cycle” consisting of a brief constructional volcanic phase lasting less than 1,000,000 years, followed by an erosional phase of some 20,000,000 years. The possibility that other oceanic islands have had comparable histories is discussed.
Discoasters of the Blue Clay (Middle Miocene) of Malta and Gozo
Authors: Hojjatzadeh Minoo 
Published: May 2009

SummaryTwenty-three species of the Family Discoasteraceae Vekshina, 1959 recovered from 18 samples of the Blue Clay at Fort Chambray, Gozo, and 31 samples from Fomm-Ir-Rih Bay, Malta, have been studied under light and scanning electron microscopes. Fourteen Middle Miocene species are reviewed, their stratigraphical ranges and importance as marker species discussed. Nine species are described as new. On the basis of the discoaster species present, a Middle Miocene age (NN.6 Discoaster exilis Zone – NN.7 Discoaster kugleri Zone) for the Blue Clay in Malta and Gozo is suggested.
Late Precambrian–Early Cambrian stratigraphic and faunal succession of eastern California and the Precambrian–Cambrian boundary
Authors: Nelson C. A. 
Published: May 2009

SummaryThe Late Precambrian and Early Cambrian strata in eastern California and Nevada can be divided into 3 facies – the eastern Craton, the White-Inyo, and the Death Valley. These 3 facies supply evidence of 3 trilobite zones – the Fallotaspis, the Nevadella and the Bonnia-Olenellus; the inter-relationships are outlined. Correlations with the Siberian Platform successions are discussed and the Precambrian–Cambrian boundary is tentatively placed within the beds of the upper Reed Dolomite in the White-lnyo Range.
The Precambrian–Cambrian boundary problem in Siberia and some general problems of stratigraphy (Preliminary Report)
Authors: Savitsky V. E. 
Published: May 2009

SummaryTwo regions are considered to be the best for the definition of the Cambrian lower boundary in Siberia – in Yakutia (the middle course of the Aldan River), in Western Prianabarye (at the Kotuikan and Kotui). The stratigraphical relationships in these 2 regions are described. Some general problems of stratigraphy are then raised (a) the need to use lithologic-facies, palaeogeography and biostratigraphy together, (b) the boundary stratotype method of delimiting chronostratigraphical subdivisions and (c) the earliest trilobite zones, the Ediacara fauna and geochronology.