bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Habberley Formation: youngest Tremadoc in the Welsh Borderlands
Authors: Fortey R. A. , Owens R. M. 
Published: May 2009

AbstractThe Habberley Formation overlies the Shineton Shale Formation in the Shelve Inlier, Shropshire, and includes the youngest Tremadoc strata known from the Welsh Basin. It probably represents deposition during the interval cut out by the sub-Arenig unconformity in North Wales, and removed by the sub-Caradoc unconformity in the Wrekin district. There is no angular unconformity between Tremadoc and Arenig in the Shelve Inlier. The Habberley Formation is likely to correlate in part with the Hunnebergian Stage of Scandinavia. It was deposited probably in a largely stagnant basin, and records a shallowing-upwards sequence, prior to the Arenig transgression of the Stiperstones Quartzite. A sparse trilobite fauna proves the presence of theAngelina sedg vickiiBiozone, and a succeeding interval is characterized byAsaphelluscf.graffi. The trilobites are briefly described; they include the first undistorted material ofAngelina sedgwvickii. The brachiopodLingulella bella(Walcott), hitherto known only from eastern Newfoundland, is described by A. W. A. Rushton.
A fault-controlled depositional model for the Aberystwyth Grits turbidite system
Authors: Wilson D. , Davies J. R. , Waters R. A. , Zalasiewiczt J. A. 
Published: May 2009

AbstractThe Aberystwyth Grits Group was the first in a series of southerly-supplied sandstone-rich turbidite systems that invaded the Welsh Basin during the Telychian Stage (late Llandovery; Silurian). Structural and stratigraphical evidence indicates that deposition of the sand-dominated parts of the system was largely restricted to the east by a zone of syndepositional faulting, now marked by a major vergence divide. Downfaulting and reverse drag along the fault hangingwall created a bathymetric low, which focused deposition of high-density, sand-carrying turbidite flows and flow components, allowing substantial thicknesses of sediment to accumulate. In contrast, low-density, mud-rich turbidites were deposited over a wider area, enhancing the topographic relief generated by uplift above the fault footwall, to form a feature which restricted the spread of the coeval easterly-supplied turbidites of the Devil's Bridge Formation.
Petrogenesis of Ordovician igneous rocks in the southern part of the Welsh Basin
Authors: Bevins R. E. , Lees G. J. , Roacht R. A. 
Published: May 2009

AbstractDuring early Ordovician times volcanic and high-level intrusive activity occurred at numerous centres across North Pembrokeshire. Previous work suggested a geochemical transition in this activity from calcalkaline through to tholeiitic with time. However, new data indicate more extensive calc-alkaline magmatism and that both magma types were coeval. The origin of the calcalkaline magmas remains equivocal, but the tholeiitic magmas appear to have been derived from a source similar to N-type MORB, variably modified by supra-subduction zone fluids, combined with some fractionation during ascent. These data are consistent with emplacement in a supra-subduction zone marginal basin.
Seismic reflection test on the granite of the Skye Tertiary igneous centre
Authors: Goulty N. R. , Leggett M. , Douglas T. , Emeleus C. H. 
Published: May 2009

AbstractWe have conducted a seismic reflection test over a short profile on the granite of the Skye Tertiary central intrusive complex. From previous gravity modelling work it had been inferred that the granite is approximately 1.5 km thick and overlies basic rocks. The seismic data indicate that the granite is at least 2 km thick at the test location. Reflection events of alternating polarity between depths of 2.1 and 2.4 km suggest that basic and acidic sheets are interlayered at the base of the granitic mass.
The origins of granulites: a metamorphic perspective
Authors: Harley S. L. 
Published: May 2009

AbstractAlthough many recent reviews emphasize a uniformity in granulite pressure–temperature (P–T) conditions and paths, granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation. A thorough survey of over 90 granulite terranes or occurrences reveals that over 50% of them recordP–Tconditions outside the 7.5 ± 1 kbar and 800 ± 50 °C average granulite regime preferred by many authors. In particular, an increasing number of very high temperature (900−1000 °C) terranes are being recognized, both on the basis of distinctive mineral assemblages and geothermobarometry. Petrogenetic grid and geothermobarometric approaches to the determination and interpretation ofP–Thistories are both evaluated within the context of reaction textures to demonstrate that the large range inP–Tconditions is indeed real, and that both near-isothermal decompression (ITD) and near-isobaric cooling (IBC)P–Tpaths are important. Amphibolite–granulite transitions promoted by the passage of CO2-rich fluids, as observed in southern India and Sri Lanka, are exceptional and not representative of fluid-related processes in the majority of terranes. It is considered, on the contrary, that fluid-absent conditions are typical of most granulites at or near the time of their recorded thermal maxima.ITD granulites are interpreted to have formed in crust thickened by collision, with magmatic additions being an important extra heat source. Erosion alone is not, however, considered to be the dominant post-collisional thinning process. Instead, the ITD paths are generated during more rapid thinning (1−2 mm/yr exposure) related to tectonic exhumation during moderate-rate or waning extension. IBC granulites may have formed in a variety of settings. Those which show anticlockwiseP–Thistories are interpreted to have formed in and beneath areas of voluminous magmatic accretion, with or without additional crustal extension. IBC granulites at shallow levels (< 5 kbar) may also be formed during extension of normal thickness crust, but deeper-level IBC requires more complex models. Many granulites exhibiting IBC at deep crustal levels may have formed in thickened crust which underwentveryrapid (5 mm/yr) extensional thinning subsequent to collision. It is suggested that the preservation of IBC paths rather than ITD paths in many granulites is primarily related to therateandtimescaleof extensional thinning of thickened crust, and that hybrid ITD to IBC paths should also be observed.Most IBC granulites, and probably many ITD granulites, have not been exposed at the Earth's surface as a result of the tectonic episodes which produced them, but have resided in the middle and lower crust for long periods of time (100−2000 Ma) following these events. The eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation.
Late Proterozoic glacial carbonates in northeast Spitsbergen: new insights into the carbonate–tillite association
Authors: Fairchild I. J. , Hambrey M. J. , Spiro B. , Jefferson T. H. 
Published: May 2009

AbstractCarbonate-rich glacial deposits from two discrete Vendian glacial periods are described. The older is represented by the 24–40 m thick Petrovbreen Member (E2) of the Elbobreen Formation which contains abundant detrital dolomite. Clasts in E2 and their possible source rocks have positive δ13C and negative δ18OPDBvalues. In contrast the carbonate mud-fraction of E2 sediments has different cathodoluminescence characteristics from clasts, slightly negative δ13C values, and higher Fe and Mn concentrations than clasts. Oxygen isotopes vary from −2.5 to +4.5‰PDB, thought to be related to various seawater–meltwater mixtures in the depositional environment. Preservation of information about glacial sedimentary environments is attributed to early diagenetic recrystallization forced by excess surface free energy (Ostwald's ripening) and coinciding with sulphate reduction.The younger glaciation is represented by the Wilsonbreen Formation (170 m) which has a distinctive glaciolacustrine Middle Carbonate Member (W2). W2 contains precipitated periglacial carbonates (with high Mn/Fe ratio): both limestone (rhythmitic and stromatolitic) and dolostone (rhythmites, stromatolites and dolomite-rich sandstones) which are compared with carbonates in modern Antarctic lakes. Evaporitic environments for dolomitic sandstones and stromatolitic dolostones are indicated by heavy oxygen isotope values (up to + 10.5‰PDB), high Na concentration and evidence for dissolved evaporites. High Mn concentration in detrital dolostones in W2 is suggestive of syn-sedimentary dolomite recrystallization in freshwater diamictites and haematitic siltstones.The carbonate–tillite association ultimately arises from the erosion of underlying carbonates which originated (in this case) under radically different climatic conditions. Glacial depositional waters then became carbonate-saturated as a result of dissolution of detrital carbonate. Massive recrystallization of glacially transported carbonate is proposed as a geologically significant process with considerable potential for palaeoenvironmental analysis. In glacial lakes carbonate precipitated in response to evaporation or photosynthesis. Carbonate precipitation as the result of seawater freezing, or in warm interglacial conditions, is not yet established. Oxygen isotope value are inconsistent (too heavy) with the presence of high-latitude meltwaters, implying that glaciation extended to low latitudes as proposed by Harland.
Caledonian nappe geometry in north-central Sweden and basin evolution on the Baltoscandian margin
Authors: Gayer Rodney A. , Greiling Reinhard O. 
Published: May 2009

AbstractStructural analysis of the Lower Allochthon in the north-central Scandinavian Caledonides has allowed the construction of restorable cross-sections consistent with the development of a foreland-propagating linked thrust system. The internal geometry of an antiformal stack, the Njakafjäll duplex, within the Lower Allochthon demonstrates tectonic shortening of c. 50% and suggests an overall predeformational width for the Lower Allochthon in this area of at least c. 130 km, and possibly considerably greater if the buried trailing edge of the Lower Allochthon lies in a comparable position to that farther south in Tröndelag. These results, combined with a stratigraphic analysis of the imbricates within the Lower Allochthon and of the adjoining Autochthon and Middle Allochthon, indicate the development, from Proterozoic through Cambrian times, of two sedimentary basins on the c. 200 km wide continental margin of Baltica bordering the Iapetus Ocean. The basins were separated by a region of basement relief, the Børgefjell domain, above which a reduced sequence of Vendian to Cambrian rocks accumulated. This Børgefjell basement high, and the similar Njakafjäll basement high to the east, subsequently became the sites of antiformal stack development. It is argued that the frequent incorporation of basement into the thrust sheets, together with the thin sedimentary fill of these basins, compared with the much greater fill in basins to the south in Jämtland and to the north of Finnmark, implies major palaeogeographic changes along the Baltoscandian margin, possibly related to early rift geometries. The apparent lack of subsequent foreland basin development in north-central Scandinavia compared with areas to the south may indicate a deeper level of thrust detachment beneath the Middle Allochthon to the north, such that any foreland basin sediments have been removed in the hangingwall and subsequently eroded. An alternative possibility is a primary absence of foreland basin development that may relate to a differing response to thrust loading by continental lithosphere which had been variably thinned during the earlier rift regime.
Microfossils from silicified stromatolitic carbonates of the Upper Proterozoic Limestone-Dolomite 'Series', central East Greenland
Authors: Green J. W. , Knoll A. H. , Swett K. 
Published: May 2009

AbstractSilicified flake conglomerates andin situstratiform stromatolites of the Upper Proterozoic (c.700–800 Ma) Limestone-Dolomite ‘Series’, central East Greenland, contain well preserved microfossils. Five stratigraphic horizons within the 1200 m succession contain microbial mat assemblages, providing a broad palaeontological representation of late Proterozoic peritidal mat communities. Comparison of assemblages demonstrates that the taxonomy and diversity of mat builder, dweller, and allochthonous populations all vary considerably within and among horizons. The primary mat builder in most assemblages isSiphonophycus inornatum, a sheath-forming prokaryote of probable but not unequivocally established cyanobacterial affinities. An unusual low diversity unit in Bed 17 is dominated by a different builder,Tenuofilum septatum, while a thin cryptalgal horizon in Bed 18 is built almost exclusively bySiphonophycus kestron.Although variable taphonomic histories contribute to observed assemblage variation, most differences within and among horizons appear to reflect the differential success or failure of individual microbial populations in colonizing different tidal flat microenvironments. Twenty-two taxa are recognized, of which two are described as new:Myxococcoides stragulescensn.sp. andScissilisphaera gradatan. sp.
Sedimentology and structure of the trench-slope to forearc basin transition in the Mesozoic of Alexander Island, Antarctica
Authors: Doubleday P. A. , Macdonald D. I. M. , Nell P. A. R. 
Published: May 2009

AbstractThe Mesozoic forearc of Alexander Island, Antarctica, is one of the few places in the world where the original stratigraphic relationship between a forearc basin and an accretionary complex is exposed. Newlydiscovered sedimentary rocks exposed at the western edge of the forearc basin fill (the Kimmeridgian–Albian Fossil Bluff Group) record the events associated with the basin formation. These strata are assigned to the newly defined Selene Nunatak Formation (?Bathonian) and Atoll Nunataks Formation (?Bathonian-Tithonian) within the Fossil Bluff Group.The Selene Nunatak Formation contains variable thicknesses of conglomeratesand sandstones, predominantly derived from the LeMay Group accretionary complex upon which it is unconformable. The formation marks emergence and subsequent erosion of the inner forearc area. It is conformably overlain by the1 km thick Atoll Nunataks Formation, characterized by thinly-bedded mudstones and silty mudstones representing a marine transgression followed by trench-slope deposition. The Atoll Nunataks Formation marks a phase of subsidence, possibly in response to tectonic events in the accretionary prism that are known to have occurred at about the same time.The Atoll Nunataks Formation is conformably overlain by the Himalia Ridge Formation, a thick sequence of basin-wide arc-derived conglomerates. This transition from fine- to coarse-grained deposition suggests that a well-developed depositional trough (and hence trench-slope break) had formed by that time. The Atoll Nunataks Formation therefore spans the formation of the forearc basin, and marks the transition from trench-slope to forearc basin deposition.
Lower Palaeozoic and Precambrian igneous rocks from eastern England, and their bearing on late Ordovician closure of the Tornquist Sea: constraints from U-Pb and Nd isotopes
Authors: Noble S. R. , Tucker R. D. , Pharaoh T. C. 
Published: May 2009

AbstractThe U-Pb isotope ages and Nd isotope characteristics of asuite of igneous rocks from the basement of eastern England show that Ordovician calc-alkaline igneous rocks are tectonically interleaved with late Precambrian volcanic rocks distinct from Precambrian rocks exposed in southern Britain. New U-Pb ages for the North Creake tuff (zircon, 449±13 Ma), Moorby Microgranite (zircon, 457 ± 20 Ma), and the Nuneaton lamprophyre (zircon and baddeleyite, 442 ± 3 Ma) confirm the presence ofan Ordovician magmatic arc. Tectonically interleaved Precambrian volcanic rocks within this arc are verified by new U-Pb zircon ages for tuffs at Glinton (612 ± 21 Ma) and Orton (616 ± 6 Ma). Initial εNd values for these basement rocks range from +4 to - 6, consistent with generation of both c. 615 Ma and c. 450 Ma groups of rocksin continental arc settings. The U-Pb and Sm-Nd isotope data support arguments for an Ordovician fold/thrust belt extending from England to Belgium, and that the Ordovician calc-alkaline rocks formed in response to subductionof Tornquist Sea oceanic crust beneath Avalonia.
Mid-Turonian ammonite faunas from northern Mexico
Authors: Kennedy W. J. , Cobban W. A. 
Published: May 2009

AbstractTuronian ammonite assemblages are described from six localities in the Ojinaga and Boquillas formations of Chihuahua in northern Mexico. These assemblages reveal the presence of the middle Turonian zones of Collignoniceras woollgari and Prionocyclus hyatti far to the south of previously documented occurrences. The Mexican collections include co-occurring collignoniceratids, known from as far north as Montana, and Tethyan euomphaloceratines and coilopoceratids. One species, Puzosia (Puzosia) serratocarinata, is new.
Maastrichtian ammonites from the Corsicana Formation in northeast Texas
Authors: Kennedy W. J. , Cobban W. A. 
Published: May 2009

AbstractPreviously undescribed collections of ammonites from the Corsicana Formation (Maastrichtian), the highest unit of the Cretaceous present in northeast Texas, U.S.A., includeEubaculites carinatus(Morton, 1834),Nostoceras (Nostoceras) majorsp. nov.,Glyptoxocerassp., andJeletzkytessp. nov., which are new records for the unit. Other ammonites areSphenodiscus lobatus(Tuomey, 1854),S. pleurisepta(Conrad, 1857),Trachyscaphites yorkensis(Stephenson, 1941),Discoscaphites conradi(Morton, 1834) andBaculites columna(Morton, 1834). Elements of the fauna are present in the Escondido Formation in Trans-Pecos Texas and northern Mexico, the Prairie Bluff Chalk in Alabama and Mississippi, the Owl Creek Formation in Mississippi, Tennessee and Missouri, and the Severn Formation in Maryland. In the U.S. Western Interior they occur in theHoploscaphites nicolletiZone, in the Fox Hills Formation.
Late Mesozoic bipolar bivalve faunas
Authors: Crame J. A. 
Published: May 2009

AbstractBipolar bivalve genera probably existed through the greater part of late Mesozoic (i.e. late Jurassic–late Cretaceous) time. Of the various theories put forward to account for their presence, those based on some form of global climatic zonation seem most appropriate. Although equatorial–polar temperature gradients were substantially less in late Mesozoic time than at the present day, high latitude regions were subjected to temperate (or even cool-temperate) climatic regimes. Macrobenthonic marine faunas may have been more susceptible to differentiation in response to these climatic patterns than nektonic ones. This is particularly so in the late Mesozoic strata of the Southern Hemisphere.
Devonian Antiarch Biostratigraphy of China
Authors: Kiang P'an 
Published: May 2009

SummaryDevonian Antiarchi in China are chiefly distributed in the S and W of the country. They are represented by 17 genera and more than 26 species, of which three genera are cosmopolitan, namely Asterolepis, Bothriolepis and Remigolepis. The early Devonian Antiarchi fauna, Yunnanolepis, Phymolepis, Zhanjilepis, is an East Asiatic fauna. The middle and late Devonian faunas are essentially endemic and associated with few cosmopolitan elements, their geological ages, however, are different from those of the cosmopolitan antiarch taxa elsewhere. As considered in the present study, six main antiarch assemblages occur: (1) Yunnanolepis-Qujinolepis assemblage (Lower Devonian), (2) Xichonolepis-Wudinolepis assemblage (Eifelian), (3) Hunanolepis tieni-Bothriolepis sinensis assemblage (Givetian), (4) Bothriolepis kwangtungensis-Bothriolepis lochangensis assemblage (Givetian), (5) Remigolepis spp. assemblages (Frasnian-Famennian), (6) Sinolepis-Asterolepis sinensis assemblage (Famennian).
A reappraisal of the conditions of deposition of the Maentwrog Beds (Upper Cambrian) at Porth Ceiriad, North Wales
Authors: Bose P. K. 
Published: May 2009

SummaryThe marine Maentwrog Beds comprise a repetition of sand and mud facies and follow a non-sequence. A shallow water depositional environment is inferred from the nature of the basal unit (with stromatolites and intraformational conglomerate), and hummocky cross-stratification and mud-draped erosion surfaces. The bulk of the formation was deposited between fair weather and storm wave base, the sand facies representing storm depositional events.
Potassium-argon ages from Tristan da Cunha, South Atlantic
Authors: McDougall Ian , Ollier C. D. 
Published: May 2009

SummaryPotassium-argon ages measured on 11 volcanic rocks, mainly lavas, from Tristan da Cunha range from 0.21 ± 0.01 to 0.01 ± 0.02 Ma, and confirm the youthfulness of this volcano, which lies on the Walvis Ridge just to the east of the crest of the Mid Atlantic Ridge.
The preservation of fossil leaves in Cretaceous volcaniclastic rocks from Alexander Island, Antarctica
Authors: Jefferson T. H. 
Published: May 2009

SummaryLeaf compression fossils are abundant within the lower Cretaceous part of the Fossil Bluff Formation in southern Alexander Island, Antarctica. They occur in lacustrine laminated siltstones with a high volcaniclastic component. During zeolite facies metamorphism of the rocks, breakdown of clay minerals, volcanic glass and calcic plagioclase generated new mineral phases. The growth of these minerals was concentrated within and around leaves: finely disseminated oxide of titanium crystallized within the organic material, a thin film of chlorite was precipitated around leaves and silica, calcite and laumontite grew disruptively between leaf cuticles. Despite relatively low levels of organic maturation the structure of the leaf cuticles was destroyed and the only details which survived were those preserved as impressions in the chorite film.
A thermokarst phenomenon on a terrace of the River Wey near Farnham, Surrey, England
Authors: Fisher P. , Rolls J. D. 
Published: May 2009

SummaryPalaeochannels developed in a terrace of the River Wey are described. Their morphology, relationship with the underlying Folkestone Sands, and the character of associated superficial deposits all suggest that the channels are examples of thermokarst phenomena, probably of Devensian age.
Partial melting of feldspathic quartzite around late Caledonian minor intrusions in Appin, Scotland
Authors: Platten I. M. 
Published: May 2009

SummaryGranophyre patches on the sites of former sedimentary feldspars in the feldspathic Appin Quartzite show that partial melting took place in the inner parts of the aureoles of late Caledonian minor intrusions. Mobilization of the melt and refractory quartz residue as a thixotropic suspension is shown to result in the formation of veins and breccias. Textures are related to the wetting of quartz/quartz grain bounderies by the eutectic melt and the later growth of crystals during cooling. From the presence of high (β) quartz coexisting with melt, minimum contact temperatures are estimated as 780°C, showing that some convective circulation of magma took place.