bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Abakaliki pyroclastics – Eastern Nigeria: new age and tectonic implications
Authors: Uzuakpunwa A. B. 
Published: May 2009

SummaryBasic to intermediate pyroclastic rocks of pre-Albian age are overlain by the Abakaliki shale of Asu River Group in Eastern Nigeria. The shale has been assigned Albian age on the basis of abundant (middle Albian?) ammonites found in it. It was folded (together with the pyroclastics) about a NE–SW trending anticlinal axis during the Santonian time. This new evidence of an early Cretaceous volcanism supports a pre-Albian rifting of the African shield prior to the opening of the Southern Atlantic. The latter event took place (probably in stages) during Albian time (i.e. less than 110 Ma ago), with a widespread marine transgression in West Africa and South America.
Proterozoic extensional deformation in the Mount Isa inlier, Queensland, Australia
Authors: Passchier C. W. , Williams P. R. 
Published: May 2009

AbstractThe earliest of four distinct phases of deformation recognized in the central part of the Proterozoic Mount Isa inlier involved brittle extensional faulting at shallow crustal levels. Extensional faulting produced stacks of imbricate fault slices, listric normal faults and characteristic tourmalinerich breccias. Structures belonging to this phase occur over a large part of the inlier and indicate an important phase of basin-forming crustal or lithospheric extension at 1750–1730 Ma. Late intense ductile deformation and tight folding of the imbricate systems destroyed part of these older structures, and obscures their existence in many parts of the inlier.
Fabric developments and the evolution of the Periadriatic Lineament in southeast Austria
Authors: von Gosen W. 
Published: May 2009

AbstractThe Periadriatic Lineament Zone which forms the boundary between the Eastern and Southern Alps in the Karawanken region of Austria has a complex history spanning the Variscan and Alpine orogenies. Variscan regional metamorphism and polyphase deformation followed by Late to Post Variscan intrusive activity with accompanying contact metamorphism affects a belt of structurally complex rocks referred to as the Eisenkappel Zone to the north of the lineament. Weak Early Alpine deformation in the Southern Alpine rocks can also be recognized in the Eisenkappel Zone. The Young Alpine intrusion of the Karawanken Tonalite was followed by lateral fault displacements associated with the formation of the Periadriatic Lineament. Late Tertiary sediments, caught up in the northward directed thrusting responsible for the uplift of the Karawanken chain, record the youngest deformation in the area.
A note on the regional context of the Loch Monar synform
Authors: Watkinson A. J. , Thiessen R. L. 
Published: May 2009

AbstractThe Loch Monar Synform folds the Sgurr Beag slide in the central northwest Highlands of Scotland. The east–west trend of the synform is oblique to the regional trend of the slide. However, when late-stage strain effects associated with superimposed folds on the synform are removed using computer techniques, the trace of the synform axial surface becomes perpendicular to the regional trace of the slide. The synform also becomes tighter and recumbent in attitude. The synform axis is parallel to strongly developed lineations. Folds of this generation appear to be localized in the vicinity of the slide. These observations suggest a model of folding associated with movement of the slide, followed by locking up of the slide and internal strain resulting in the superimposed folds and rotation of the synform.
The disequilibrium partial melting and assimilation of Caledonian granite by Tertiary basalt at Barnesmore, Co. Donegal
Authors: Kitchen D. E. 
Published: May 2009

AbstractA regional Tertiary basaltic dyke swarm intensifies within a Caledonian granite at Barnesmore, Co. Donegal. Rapid heating along the contact of one (possible feeder) dyke resulted in disequilibrium partial melting of granite wall-rock and the generation of a range in melt composition by the in situ melting of feldspar. The compositional variability of the melt is preserved in a glass containing feldspar spherulites and other quench phases which suggest rapid cooling. During partial melting the trace elements, Rb, Sr, and Ba were mobile and have been concentrated in glassy melted granite close to the contact of one dyke. The textures, mineralogy and geochemistry of dolerite in two dykes indicate localized bulk contamination and mixing with melted granite. This had a particularly marked effect on the crystallization of pyroxene and resulted in a wide range in mineral composition reflecting the degree of contamination. The intensification of a regional dyke swarm in well-jointed granite might control the siting of some major intrusive centres. Granite melted and mixed with basaltic magma may contribute to the evolution of granites in such centres.
Westphalian alluvial plain sedimentation, Isle of Arran, Scotland
Authors: Kirk M. 
Published: May 2009

AbstractFacies analysis suggests that Westphalian (Upper Carboniferous) Coal Measure sequences on the Isle of Arran, Scotland, were deposited in a proximal alluvial plain environment close to the basin margin. Detailed examination of well exposed coastal sections has revealed the existence of six laterally and vertically interrelated sedimentary facies. Facies 1 to 3 are interpreted as fluvial channel deposits. Low sinuosity multistorey (facies 1), low sinuosity vertically accreted (facies 2), and rare high sinuosity laterally accreted channel deposits (facies 3) are developed. Associated overbank sediments comprise the deposits of crevasse splays (facies 4), flood plains (facies 5) and shallow lakes (facies 6). In terms of the spatial distribution of facies, a relatively high proportion of fluvial channel and floodplain deposits (facies 2 and 5) occur in the more proximal sequence at Laggan compared with the more distally located sequence occurring at Corrie. Palaeocurrent measurements from fluvial channel sandstones indicate that sediment source areas and the Westphalian basin margin lay to the north and northwest. Down palaeoslope towards the southeast, normal coal-bearing Westphalian sediments formed penecontemporaneously on the Scottish mainland in Ayrshire.A sedimentological model is presented for the proximal non-coal-bearing Westphalian sequences of Arran. This model can explain the differences observed between the Arran sediments, and contemporaneous normal coal-bearing Westphalian sediments of the Scottish mainland.
Quartz-spessartine metasediments (coticules) and their protoliths in North Wales
Authors: Bennett M. A. 
Published: May 2009

AbstractThin beds and small pods of quartz-spessartine metasediments (coticules) occur in pelites of the Gamlan Formation (Cambrian) of the Harlech Dome. The original microfabric of these sediments has been largely destroyed by recrystallization under low greenschist facies conditions. The quartz-spessartine pods occur throughout the pelites and appear to have formed by the metamorphism of diagenetic Mn-carbonate concretions. The thin beds of quartz-spessartine rock appear to have formed by the metamorphism of a protolith which was deposited rapidly and repeatedly over a wide area. Although there is no direct evidence of the nature of this protolith, the presence of altered Mn-carbonate-rich tuff beds in anchizonal mudstones of similar age in the St Tudwal's Peninsula suggests that the bedded quartz-spessartine rocks are, in fact, metamorphosed Mn-carbonate-rich tuff units. Both the bedded and podiform quartz-spessartine metasediments appear to have formed by reaction between clay minerals and Mn carbonates of earlier diagenetic origin.
Lower Cambrian anabaritids from south China
Authors: Conway Morris S. , Menge Chen 
Published: May 2009

AbstractAnabaritids are a distinctive group of early skeletal fossils, with tri-radially symmetrical tubes. They occur in the earliest Cambrian deposits, and seem to be especially characteristic of the Tommotian strata and putative pre-Tommotian units (e.g. Manykay horizon). A detailed redescription ofAnabarites rotundusQian from near Kuanchuanpu, Shaanxi Province emphasizes the degree of morphological variation. New data on shell composition suggest a bilayered structure, the outer unit composed of fibres parallel to growth lines, overlying a distinctive inner lamella with a chevron ultrastructure. Tentative evidence for anabaritids possibly being operculate is presented, the putative operculum being a simple convex disc. More poorly preserved anabaritids from the Yangtze Gorges (Hubei Province) and Meishucun (Yunnan Province) are referred toA. trisulcatus. All these Chinese occurrences of anabaritids are consistent with a lower Tommotian age of the associated faunas, but reliable and precise correlations with other Precambrian-Cambrian boundary sections remain inconclusive.
Lower Cambrian coeloscleritophorans (Ninella, Siphogonuchites) from Xinjiang and Shaanxi, China
Authors: Morris S. Conway , Chapman A. J. 
Published: May 2009

AbstractNinella tarimensisfrom the Lower Cambrian Yurtus Formation of western Xinjiang, China, is shown to be a relative of the halkieriids and siphogonuchitids. These are known principally from dispersed sclerites, presumably secreted by slug-like organisms that were an abundant component of the Cambrian benthos. The sclerites ofN. tarimensisare relatively small, strongly recurved and usually possess an upper surface ornamented with transverse sculpture. The lower surface is more or less smooth and is joined to the upper surface via steep faces that may be grooved. The apertural region is quadrate in outline and bears a circular foramen.Ninellais fairly widespread and is known from elsewhere in China (Guizhou and Shaanxi Provinces) and from Kazakhstan. A brief description of the siphogonuchitid scleritome is also presented, based on dispersed sclerites and shells from the Lower Cambrian of Shaanxi Province, China. Formal synonymy of the sciotaxaSiphogonuchites, Dabashanites, Lopochites, andMaikhanellaasSiphogonuchitesis proposed.
Quaternary tectonics at the eastern border of the Bohemian Massif: new outcrop evidence
Authors: Leichmann Jaromir , Hejl Ewald 
Published: May 2009

AbstractRecently, an outcrop with clear evidence for Quaternary faulting has been discovered in the eastern part of Bohemian Massif, 25 km southwest of Brno (Moravia, Czech Republic). Basement serpentinite, fluvial gravels, loess and young scree are affected by a steep NNW–SSE trending fault. The geological situation of the outcrop is described for the first time in this article.
The Pan-African Toro Complex (northern Nigeria): magmatic interactions and structures in a bimodal intrusion
Authors: Déléris J. , Nédélec A. , Ferré E. , Gleizes G. , Ménot R.-P. , Obasi C. K. , Bouchez J.-L. 
Published: May 2009

AbstractThe Toro Complex is one of the Pan-African Older Granites of Nigeria, first described as a reversely zoned pluton made of a central dioritic mass surrounded by a broad granitic rim. It has been thoroughly reinvestigated both from the petrographic and structural points of view, with the help of systematic anisotropy of magnetic susceptibility (AMS) measurements. The granite main body is a hornblende–biotite porphyritic monzogranite characterized by an early submagmatic fabric displaying a concentric pattern of foliations and west plunging lineations (stage 1). This fabric is overprinted by a later one due to solid-state strain along north-south subvertical dextral shear zones (stage 2). In the vicinity of the diorite, an evengrained granite displays magmatic structures that are contemporaneous with this strike-slip event. The diorite–granite contact is a complex zone where field, petrographic and geochemical data enable recognition of the effects of mixing and mingling between a mafic and a felsic magma. Tonalites cropping out within this contact zone are interpreted as hybrid rocks. The reverse zonation of the diorite itself is also the result of some hybridization process. Magmatic interactions mainly resulted from in situ infiltration of granitic liquid into the dioritic mass. The detailed history of this bimodal intrusion began with the emplacement of the granitic magma acquiring a first stage fabric. Before full crystallization of the granitic core, intrusion of the dioritic magma permitted reheating of the granitic magma that then crystallized with specific structural characters. The second stage structures, whether characterized by magmatic fabric near the diorite or by solid-state strain features in north–south shear zones elsewhere in the granite, are related to late Pan-African dextral strike-slip tectonics in the basement of northern Nigeria. The bimodal Toro Complex is therefore considered as a late Pan-African syntectonic pluton.
Low-pressure, high-temperature metamorphism in a compressional tectonic setting: Mary Kathleen Fold Belt, northeastern Australia
Authors: Reinhardt J. 
Published: May 2009

AbstractThe Mary Kathleen Fold Belt in northeastern Australia consists of highly deformed, Mid-Proterozoic sedimentary and volcanic sequences as well as intrusives, which were metamorphosed under low-pressure, high-temperature conditions. In the light of current controversy on tectono-thermal settings of low-pressure metamorphic terrains, the interrelations of progressive deformation and metamorphism have been closely examined. Remarkably, there is no direct evidence for syn-metamorphic extensional deformation nor is any significant intrusive activity recorded.Syn-metamorphic structures indicate lateral, bulk coaxial shortening of at least 50–60%. Tight upright folds, pervasive axial planar fabrics, undulating fold axes, and a vertical mineral lineation characterize this deformation. The metamorphic textures, particularly those in andalusite- and/or cordierite-bearing schists, reveal the sequential growth of metamorphic minerals that was synchronous with progressively increasing bulk rock strain. The corresponding metamorphic reactions constrain a prograde P–T path segment that crossed the andalusite and sillimanite stability fields while temperature and pressure increased. After reaching the metamorphic peak, the region cooled down near-isobarically, before major decompression occurred. The prograde–retrograde P–T path forms a complete anticlockwise loop.Due to the lack of evidence for crustal thinning and large-scale magmatism in the upper crust, alternative models are discussed in order to explain the transient high geothermal gradient. These are in particular convective thinning of the lithospheric mantle and fast decompression of crustal sections, possibly linked to tectonic processes preceeding the low-pressure/high-temperature orogenic event.
Chemistry and petrological evolution of the Lastarria volcanic complex in the north Chilean Andes
Authors: Naranjo José A. 
Published: May 2009

AbstractThe Lastarria volcanic complex, along the northern Chile–Argentina border, includes three morphostructural components: Southern Spur, Lastarria (the highest cone, 5697 m) and Negriales (a geographically associated lava field, 5.4 km3). Petrographically, the Lastarria complex consists of pyroxene andesites and pyroxene–amphibole dacites. The whole-rock geochemistry shows a bimodial silica variation between 57 and 68%, with peaks at 59–60% and 61.62% SiO2. Petrographie and chemical data indicate different magmatic sources for Lastarria and Negriales. Whole-rock geochemistry can be explained by crustal contamination and crystal–liquid fractionation, with differences in storage times in magma chambers being a major controlling factor. Strong textural, mineralogical and chemical evidence for magma mixing, shortly before explosive eruptions at Lastarria, suggests that this process may have triggered the violent eruptive volcanic activity which characterizes the latest stages of the main cone. Abundant bombs of banded clear pumice and dark scoria in pyroclastic flow deposits are the texturally heterogeneous products resulting from incomplete mixing homogenization.
The ichnofauna of the Skiddaw Group (early Ordovician) of the Lake District, England
Authors: Orr Patrick J. 
Published: May 2009

AbstractDeep-marine strata of the Skiddaw Group, deposited in high southerly palaeolatitudes on the northern margin of Eastern Avalonia in the early Ordovician, contain a diverse ichnofauna dominated by examples of fodinichnia. This includesAlcyonidiopsis pharmaceus, several ichnospecies ofChondrites, Dictyodora zimmermani, Glockerichnus radiatus, Gordia marina, Ixalichnus enodius, two or possibly three ichnospecies ofPhycodes, Planolites montanus, Volkichnium volki, an ‘arthropod-produced? repichnion’, ‘paired pits’, ?Gordiaaff.marina, ‘thinly-walled, looping, burrows’ and burrows ofPlanolites/Palaeophycusaffinity.Stellascolites radiatusEtheridge, 1876 is reassigned to the ichnogenusGlockerichnusPickerill, 1982 asGlockerichnus radiatus(Etheridge, 1876).Several of the ichnotaxa are present in other ichnofaunal assemblages of early Ordovician age which were also emplaced at high southerly palaeolatitudes. The relatively high diversity of this ichnofaunal assemblage supports suggestions that models of the rate at which the deep-marine environment was colonized during the early Phanerozoic are in need of revision.
Bedform movement in a marine tidal delta: air photo interpretations
Authors: Harris P. T. , Jones M. R. 
Published: May 2009

AbstractMorphological changes in bedforms composing a tidal delta at the northern entrance to Moreton Bay, Queensland have been studied by examining aerial photographs spanning a 26-year time period. The aerial photographs show the movements of 51 different sand-bank crestlines, and the morphological characteristics of both sand banks and sandwaves. From the orientation of sandwave crests to the sand-bank crestlines, zones of ebb- and flood-dominance in sand-transport direction are distinguished. The migration directions of the sand banks are predicted by considering the cross-sectional asymmetry of the sand banks together with their adjacent ebb/flood zones of net sand transport. The reliability of the predictions is tested by comparisons with sequential air photo data. When applied to 53 bedforms, the predictions achieved a high success rate, with 45 predicted migration directions matching those observed on the sequential aerial photographs. Bedform movement can be predicted, therefore, for any water depths in which submarine bedforms can be clearly seen on aerial photographs (< 10 m).Based upon their mobility, sand banks are classified into three categories: dynamic sand banks, which change quickly (within 2 years) and which have migration rates that are non-uniform along the bank crestline; progressive sand banks, which change slowly (from 2–10 years) and have migration rates that are uniform along their crestlines; and immobile sand banks, which change only over time intervals which exceed 10 years. Changes in sand-bank morphology occur by migration of the crestline together with growth and decay, and are considered to be linked with changes of larger ebb- and flood-dominant zones of net sand transport. The three different sand-bank types are characterized by distinctive heights, crestline lengths and wavelengths. They occur in different locations within Moreton Bay, possibly related to distance from external sand supplies and to relative tidal current and surface wave energy levels.
Alluvial channel bank-collapse phenomena in the Old Red Sandstone Hitra Group, Western Central Norway
Authors: Bøe R. 
Published: May 2009

AbstractThe Old Red Sandstone (ORS) on the island of Hitra forms an approximately 1350 m thick succession of alternating continental mudstones, sandstones and conglomerates of possibly latest Silurian to Devonian age. Within the middle part of this succession, just above a major, scoured surface, a spectacular slump feature was observed. The phenomenon is interpreted as a unit of overbank/channel bank mudstones which, because of undercutting and liquidization, caved into a low sinuosity river channel. The Hitra sequence is the only one in the Norwegian ORS where such phenomena have as yet been identified.
Studies of tooth implantation in fossil tetrapods using high-resolution X-radiography
Authors: Fraser N. C. , Shelton C. G. 
Published: May 2009

AbstractThe concept that reptilian tooth implantations fall neatly into a number of separate categories which can be used in phylogenetic studies is called into question. The use of microfocal X-radiography in preliminary studies of reptilian dentitions reveals that, at least in sphenodontids, there is no clear distinction between acrodonty and pleurodonty. Although the technique is used here specifically in connection with microvertebrates, it may have considerable potential in evaluating internal structures in a wide range of fossils.
Upper Ordovician cliefdenellids (Porifera: Sphinctozoa) from China
Authors: Webby B. D. , Baoyu Lin 
Published: May 2009

AbstractAporate sphinctozoan sponges of the Family Cliefdenellidae Webby, 1969, are described for the Upper Ordovician (Ashgill) of northern and northwest China, including the new genusKhalfinaeaand a new speciesK. shaanxiensis. They are characteristic cliefdenellids with conico-cylindrical and branching forms, a single central tube defined by a thickened, sieve-like endowall, and a filling of irregularly orientated astrorhizal canals, vesicles and thickened (?trabecular) tissueTaxonomic relationships of the other cliefdenellids are also discussed. The conception of the genusCliefdenellaWebby, 1969, is restricted to those forms with massive, hemispherical to explanate form and multiple, bundled vertical excurrent canal-clusters, and the new genusRigbyetiais introduced to include conico-cylindrical and branching forms with a central tube composed of a single, vertical, bundled, excurrent canal-clusterIn terms of their biogeographical record, the cliefdenellids have a restricted distribution in the Upper Ordovician (middle Caradoc-Ashgill) ‘fold-belt’ successions of the Palaeo-Pacific region (eastern Australia, Alaska and northern California) and in Asia (northern China, and in the Chinese and Soviet Altai)
Ground melting and ocellar komatiites: a lead isotopic study at Kambalda, Western Australia
Authors: McNaughton N. J. , Frost K. M. , Groves D. I. 
Published: May 2009

AbstractStratigraphically and geographically restricted ocellar komatiite flows at Kambalda, Western Australia, appear to represent the products of ground melting of sulphidic sediments by komatiites in lava channels that localized the Fe–Ni–Cu sulphide ores. An immiscible sulphide liquid formed and gravitationally separated from the melted sediment (xenomelt), the resultant buoyant silicate liquid being partly or wholly assimilated by the turbulently convecting komatiite magma. Rarely, the xenomelt gravitationally migrated to the top of flows, and overflowed into the less turbulent lava levees where it collected to form a separate layer overlying a komatiitic layer within a single flow. There was selective preservation of the hybrid felsic layer, as an upper ocellar unit within an ocellar komatiite flow, in lava levees flanking lava channels. The ocellar unit is enriched in elements previously concentrated in the sediments, and shows U–Th–Pb isotopic systematics akin to the underlying sediments. Moreover, the partitioning relationships of U and Pb between the immiscible xenomelt and sulphide liquid enhances the range of U/Pb ratios for components of the ocellar unit, thus allowing sufficient spread of modern uranogenic Pb isotopic ratios to form isochrons, albeit imprecise ones. The range and similarity of model Th/U data from these flows (2.8−3.9) and adjacent sulphidic sediments (2.3−4.4; mostly 2.8−3.9) contrasts with the generally invariable Th/U within Kambalda ultrabasic–basic flows (3.6−3.9), and further supports the ground-melting hypothesis.