bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fractionation in a zoned monzonite pluton: Mount Dromedary, southeastern Australia
Authors: Smith I. E. M. , White A. J. R. , Chappell B. W. , Eggleton R. A. 
Published: May 2009

AbstractMount Dromedary pluton is one of several predominantly monzonite plutons and smaller intrusive bodies which constitute the Dromedary igneous complex in southeastern New South Wales. The pluton exhibits a striking arrangement of petrographically, but not always chemically, distinct zones ranging from mafic monzonite at the outside to quartz monzonite in the centre. The rocks display a mineralogical and geochemical integrity which indicates a consanguineous relationship. Minor compositional discontinuities between zones, together with observed and inferred minor intrusive zone boundaries, suggest that each zone has to some extent evolved independently. Negative Eu anomalies in REE abundance patterns show that some of the zones have been affected by fractionation of feldspar, but complementary accumulates are not found at the present levels of exposure. The pattern of zoning can be explained by a process of shallow fractional crystallization in which variations within zones are the result of lateral accretion of alkali feldspar as well as settling and/or lateral accretion of mafic phases at lower levels in the intrusion and upward displacement of fractionated magma. The parental magma of the pluton probaby originated by partial melting of an alkali basalt composition with an amphibolite mineralogy at the base of the crust.
A new 14C age for the Oruanui (Wairakei) eruption, New Zealand
Authors: Wilson C. J. N. , Switsur V. R. , Ward A. P. 
Published: May 2009

AbstractThe Oruanui eruption was the largest known outburst of Taupo volcano, New Zealand, and is among the larger Quaternary eruptions documented. The eruption deposits are variously known as the Oruanui, Wairakei, Kawakawa Tephra, or Aokautere Ash formations, and represent a bulk volume probably exceeding 500 km3. Four new 14C age determinations on carbonized vegetation in the non-welded Oruanui ignimbrite are combined to give a conventional age of 22590±230 yr b.p. Compared with the previously accepted figure of 20000 yr b.p., this new age resolves the anomaly of apparently older 14C ages being obtained from a demonstrably younger New Zealand deposit, and strengthens correlation of this eruption with an Antarctic ice-core acid anomaly. The trace of this eruption has great potential as a time-plane marker in the Antarctic just prior to the last glacial maximum. The close similarity in ages between the Oruanui and a comparable sized eruption (Ito/Aira-Tn) in Japan suggests that this period of activity may represent the best chance of resolving any linkages between large-scale explosive silicic volcanism and climate changes.
Stratigraphy and structures of the Nahavand region in western Iran, and their implications for the Zagros tectonics
Authors: Alavi Mehdi , Mahdavi M. A. 
Published: May 2009

AbstractSeveral rock stratigraphic successions, metamorphosed and non-metamorphosed, are found to be similar and/or identical with each other across the so-called ‘Main Zagros Thrust’. Stratigraphic successions form thin allochthonous sheets carried from northeast to southwest by numerous low-angle thrust faults of either ductile to brittle-ductile type or brittle type. Similarities in lithic and faunal characteristics of the stratigraphic units and in the style of structural deformation across the ‘Main Zagros Thrust’ imply that either the suture between the Afro-Arabian and Iranian lithospheric plates is not located in the Nahavand region or, if it is, it must be buried under several thrust sheets.
New records of Devonian plants from southern Victoria Land, Antarctica
Authors: McLoughlin S. , Long J. A. 
Published: May 2009

AbstractAn assemblage of fossil plants is here recorded from the Middle Devonian Beacon Heights Orthoquartzite and overlying Aztec Siltstone (Taylor Group), of the Cook Mountains and Skelton Névé regions, southern Victoria Land, Antarctica. The Beacon Heights Orthoquartzite exposed in the southern Cook Mountains yielded specimens of the lycopods Haplostigma lineare, Malanzania sp., and Archaeosigillaria sp. cf. A. caespitosa. The Aztec Siltstone flora contains Praeramunculus alternatiramus and H. lineare.
Silurian conodont-based correlations between Gotland (Sweden) and Saaremaa (Estonia)
Authors: Jeppsson L. , Viira V. , Männik P. 
Published: May 2009

AbstractCorrelations between the Silurian successions of Gotland and the East Baltic are based on the narrowest stratigraphic units that can be distinguished in both areas. In order further to increase precision, true ends of ranges in measured sections have been used instead of ‘pooled’ formational faunas, where outcrops and collections permit. Some previous correlations are confirmed. In other cases, there are considerable changes both in levels of correlation and in precision. The major differences are found mostly when one or more of the major gaps have remained unrecognized and stratigraphic units therefore have been extended and translated upwards or downwards. At least some of these gaps decrease in magnitude southwards in Estonia. Gaps at these levels are also noted on Gotland, although they are small and probably do not extend across the island. The patterns through time of deposition (during secundo episodes) and gaps (during primo episodes) agree very well with what can be predicted from a model of oceanic and climatic cyclicity.
Turbidite to storm transition in a migrating foreland basin: the Kendal Group (Upper Silurian), northwest England
Authors: King Louisa M. 
Published: May 2009

AbstractThe uppermost Windermere Supergroup (Kendal Group) of northwest England records the passage from Wenlock and lower Ludlow deep water ‘flysch’ deposits to upper Ludlow and Přídolí shallower water ‘molasse’ deposits within an evolving foreland basin. An upwards progression is preserved from oxygen-poor basin-slope turbidite deposits through more oxygenated, bioturbated dilute density flow deposits, to storm and wave-influenced sediments. The storm-influenced sediments display hummocky cross-stratification, aSkolithosichnofacies, shelly lags, and symmetrical wave ripple cross-lamination. Convolute lamination increases in magnitude and frequency in the upper part of the sequence, apparently nucleated above ripple crests. Tropical hurricanes probably controlled storm deposition, as suggested by late Silurian palaeogeographic reconstructions. Structures in the heterolithic muddy siltstones suggest deposition in a lower energy, wave-influenced setting. Mud-drapes, short wavelength symmetrical ripples and multi-directional ripple cross-lamination are common. The Kendal Group shows a regional palaeocurrent distribution consistent with an arcuate basin geometry, bounded to the northwest and northeast by topographic slopes. As well as a temporal trend, facies and faunal diachroneity imply a southwards migration of the foreland basin depocentre through Ludlow and Přídolí time, probably ahead of a rising mountain front to the north. The increase in pre-lithification sediment disturbance may reflect greater earthquake activity as this mountain front advanced and the basin began to invert.
Cambrian stratigraphy of St Tudwal's Peninsula, Gwynedd, northwest Wales
Authors: Young T. , Martin F. , Dean W. T. , Rushton A. W. A. 
Published: May 2009

AbstractLithostratigraphic units of early to late Cambrian age established by T. C. Nicholas in 1915 in the St Tudwal's Peninsula are revised. They comprise, in ascending order: Hell's Mouth Formation (> 190 m); Trwyn y Fulfran Formation (37 m);Cilan Formation (400 m); Ceiriad Formation (40 m seen); Nant-y-big Formation (> 110 m seen); Maentwrog Formation (in part, 50 m seen, an estimated 250 m concealed); Ffestiniog Flags Formation (in part,c. 120m seen). The ‘calcareous grit’ at the top of Nicholas's Nant-pig Mudstones spans the unconformable boundary between the Nant-y-big and Maentwrog formations. Previously described limestone clasts in the ‘grit’ are probably erosional remnants of anin situbioclastic limestone bed; their contained trilobites include genera and species found in the Andrarum Limestone (late Middle Cambrian) of Scania, Sweden. Acritarchs are documented and compared particularly with those from eastern Newfound-land. Those from the highest part of the ‘calcareous grit’ includeCymatiogaleasp. and are of late Cambrian age. One new species,Heliosphaeridium? llynenseMartin, comes from the lower part of the Nant-y-big Formation (middle Middle Cambrian), where it appears a little earlier than theAdara aleaBiozone.
A search for shocked quartz grains and impact ejecta in early Silurian sediments on Gotland, Sweden
Authors: Schmitz Birger , Jeppsson Lennart , Ekvall Johan 
Published: May 2009

AbstractAll bentonite and bentonite-resembling layers thicker than a few millimetres from a 120m-thick Early Silurian sequence on Gotland, Sweden, were searched for shocked quartz grains of comet or asteroid impact origin. Although more than 200000 quartz grains from 86 bentonite samples were studied, not one single grain with multiple planar shock features was found. The studied sequence represents sedimentation during a period of about 2 million years. Impact frequencies, estimated from the cratering record and astronomical observations, indicate that during a 2-myr- period on average 20 comet or asteroid bodies larger than 0.5 km in diameter strike the Earth. The number of smaller impacting bodies is many times higher. In the light of this high frequency of impacts, the absence of any shocked-quartz-bearing fallout layer in our sequence indicates that lateral spreading of such ejecta is relatively restricted during small- and medium-scale impact events.The results also show that shocked quartz in general is absent or extremely rare in volcanic ash. This strengthens the case for an impact-related origin of shocked quartz grains in the Cretaceous–Tertiary boundary days.
Mylonitic mafic granulite in fault megabreccia at Clarke Head, Nova Scotia: a sample of Avalonian lower crust?
Authors: Gibbons Wes , Murphy J. Brendan 
Published: May 2009

AbstractThe Clarke Head fault megabreccia was produced within a major Late Palaeozoic transcurrent structure (the Minas fault system) which separates the displaced Meguma terrane of southern Nova Scotia from rocks more typical of the Avalon Superterrane. A large clast of anomalously high grade metabasite embedded in the clay matrix of the fault megabreccia displays a fresh granulite facies mineralogy (2-pyroxene + garnet + plagioclase) and mylonitic to ultramylonitic textures induced by anhydrous shearing deep in the roots of the fault zone. Whole rock geochemistry reveals the granulite protolith to have been a continental, within-plate mafic magma transitional between theoleiitic and alkaline. The original geochemical signature has survived strong dynamic recrystallization at granulite grade. Well-preserved REE abundances testify to a lack of metasomatic fractionation during high grade shearing under water-absent conditions. Sm—Nd data indicate that the basic granulite has a TDM age of c. 1 Ga. Isotopic comparisons with adjacent areas reveal similar TDM ages both north and south of the Minas fault system. The high grade clast may be typical of the lower crust in Nova Scotia and is thought to offer a rare window into the deep crust of the Avalon Superterrane in North America.
Phosphatized soft tissues in bivalves from the Portland Roach of Dorset (Upper Jurassic)
Authors: Wilby Philip R. , Whyte Martin A. 
Published: May 2009

AbstractPhosphatized soft tissues are preserved in abundance in the trigoniids (Bivalvia) Laevitrigonia gibbosa and Myophorella incurva from the Portland Roach (Upper Jurassic) of Dorset. Cellular structures are preserved and fossilization is almost exclusively the result of a dense coating of mineralized microbes. Phosphatized soft tissues are restricted entirely to those trigoniids whose valves remained tightly closed after death. Only in these specimens was sufficient phosphorus concentrated by the decay of their most ‘labile’ soft tissues to trigger the precipitation of apatite in and around microbes infesting their more ‘refractory’ soft tissues. The absence of fossilized soft tissues in the rest of the fauna implies that phosphatization was very taxon-specific.
The Kunene complex, Angola/Namibia: a composite massif-type anorthosite complex
Authors: Ashwal Lewis D. , Twist David 
Published: May 2009

AbstractThec. 15000 km2,c. 2 Ga Kunene complex of southern Angola and northern Namibia is one of the world's largest occurrences of anorthositic rocks, rivalled only perhaps by the Lac St Jean massif of the Grenville Province in Quebec. We report here the results of a detailed field and laboratory study of a 100 km2area in the northern part of the complex. Coarse grained (av. 1–2 cm) anorthosite and leucotroctolite are the predominant rock types, although colour index varies between 0 and 50, averaging about 10. Ultramafic rocks are totally absent. Typical mineralogy is: plagioclase (An57–76) + olivine(Fo64–71) + orthopyroxene(En65–74) + clinopyroxene ± Fe—Ti oxides ± apatite. Textures are dominantly massive, although weak, impersistent, magmatic lamination with nearvertical dip and unsystematic strike is also present. Other magmatic features include plagioclase and orthopyroxene megacrysts, block structure, mortar texture, and anorthositic dykes. Metamorphic effects are minimal or absent. All of these attributes are similar to those found in typical massif-type anorthosites. Since comparable features are present over large areas elsewhere in the complex, we suggest that Kunene should be considered analogous to a large, composite, massif-type anorthositic intrusive complex, rather than to a large, single or composite mafic layered intrusion such as Bushveld, as has been previously suggested or assumed. This interpretation is supported by satellite imagery, which shows the outlines of several individual anorthositic plutons, one of which clearly encompasses our field area.
Magnetic remanence in the Chalk of eastern England: an unusually resistant VRM?
Authors: Borradaile Graham J. 
Published: May 2009

AbstractA single component, natural remanent magnetization (NRM) is carried largely by pseudosingle domain magnetite in the Cretaceous Lower Chalk and Red Chalk of eastern England. The Red Chalk also records the same direction in haematite. Most of the ferro-magnetic minerals occur as primary clastic or early diagenetic grains. A stable remanence component is resistant to demagnetization, and is carried by both magnetite and haematite. Nevertheless, it has a steep inclination close to the present Earth's field and it is too steep for the previously reported palaeolatitude of these rocks at the time of sedimentation. A postglacial slump breccia scatters the ChRM but also provides some evidence of viscous, partial magnetic overprinting during slumping. Despite its resistance to thermal and alternating field demagnetization the characteristic remanent magnetization (ChRM) is probably a young Bruhnes epoch viscous remanent remagnetization (VRM).
Intra-Ordovician deformation in southeast Ireland: evidence from the geological setting, geochemical affinities and U—Pb zircon age of the Croghan Kinshelagh granite
Authors: Gallagher V. , O'Connor P. J. , Aftalion M. 
Published: May 2009

AbstractThe Croghan Kinshelagh alkali granite intrudes a cleaved volcano-sedimentary sequenceon the border of counties Wicklow and Wexford in southeast Ireland. U-Pb dating of zircons fromthe granite indicate a mid-Caradoc emplacement age of 454 ± 1 Ma. The Duncannon Group hostrocks form the southwestern end of the Avoca Volcanic Belt, a Mid-Ordovician (Caradoc) sequenceof acid and intermediate lavas and volcaniclastics. Dolerite dykes intrude the granite; elsewhere in theregion dolerites are generally associated with volcanic rocks. The main, Dl deformation within theDuncannon Group rocks is manifest as a steep Dl cleavage generally regarded as a product of LateCaledonian regional deformation in southeast Ireland. The Croghan Kinshelagh granite showsstrong geochemical coherence with subalkaline varieties of the Caradoc volcanic rocks; relativelyhigh Th, Y, Nb and REE contents set it apart from any other known granite type in southeastIreland. Together with the geochemical evidence, the age determination of 454 Ma indicates that theCroghan Kinshelagh granite was generated and emplaced during Ordovician volcanism in southeastIreland. Volcanism was closely followed by penetrative deformation and emplacement of the granite.The intra-Ordovician deformation may have been a consequence of closure of the Iapetus Ocean ormore localized events such as accretion on the hanging wall of the subduction zone. The age of theCroghan Kinshelagh granite provides an important datum for Ordovician volcanism and subductionin southeast Ireland.
The Cenomanian-Turonian Boundary Event in northern Spain
Authors: Paul C. R. C. , Mitchell S. , Lamolda M. , Gorostidi A. 
Published: May 2009

AbstractA sparse but moderately diverse nannoflora is recorded through the Cenomanian-Turonian Boundary Event (CTBE) at Menoyo, Spain and allows recognition of the late CenomanianEiffellithus turriseiffeliiZone and the early TuronianQuadrum gartneriZone, as well as five significant nannofossil bioevents associated with the CTBE. Carbon isotopes record a modest excursion which lasted 250–270 thousand years (ka) in three phases, buildup (105 ka), plateau (126 ka) and recovery (42 ka). Acid insoluble residue values imply that sea level rose through the buildup phase, indicated by a reduction in the accumulation rate of siliciclastic sediment. However, oceanic productivity apparently declined through the CTBE, indicated by reduction in accumulation rates of total carbonate and intact coccoliths to less than a quarter of their initial values. These patterns are very similar to those found through the CTBE at Dover, England and reflect widespread not local effects. A combination of lithological changes, seven key bioevents, and details of the δ13C curve, allows us to suggest a bed-by-bed correlation through the CTBE between Dover and Menoyo, demonstrating the practicality of cyclostratigraphy for international correlation at a precision of ± 10 ka. Graphic correlation produces a straight line fit despite wide fluctuations in sediment accumulation rates at both localities. This can only occur if changes were in phase and of similar magnitudes at both localities, again suggesting widespread, perhaps global, control.
First post-Triassic temnospondyl amphibians from the Shan-Thai block: intercentra from the Jurassic of peninsular Thailand
Authors: Buffetaut Eric , Raksaskulwong Lertsin , Suteethorn Varavudh , Tong Haiyan 
Published: May 2009

AbstractTwo temnospondyl intercentra from non-marine middle Jurassic rocks at Mab Ching, in the southern peninsula of Thailand, are the first remains of post-Triassic labyrinthodont amphibians to be reported from the Shan-Thai block. They closely resemble an intercentrum recently reported from the middle Jurassic of the Khorat Plateau of northeastern Thailand, which is part of the Indochina block. Although the Mab Ching specimens are too fragmentary to warrant a precise identification, they confirm that temnospondyl amphibians were widespread on the various Asian continental blocks in the Jurassic.
The base of the Jurassic System: new data on the first appearance of Psiloceras planorbis in southwest Britain
Authors: Hodges Peter 
Published: May 2009

AbstractRecent collecting in the Lower Lias of localities at St Audrie's Bay, north Somerset, Sedbury Cliff, Gloucester and Lavernock Point, South Glamorgan has yielded Psiloceras planorbis (J. de C. Sowerby) in beds considered by some to be of Rhaetian, Triassic age. These are the earliest records of this ammonite to date in southwest Britain. Evidence is provided of a major facies change at the top of the pre-planorbis beds followed by the diachronous first occurrence of Psiloceras planorbis. These new data have implications for the use of earliest occurrence of Psiloceras planorbis as a chronostratigraphic marker in defining the base of the Jurassic System, and for the definition of the base of the Hettangian Stage in the recently proposed candidate Global Stratotype Section at St Audrie's Bay.
The earliest Ordovician nematophorid graptolites: taxonomy and correlation
Authors: Erdtmann B.-D. 
Published: May 2009

AbstractThe earliest nematophorid (planktic) dendroid graptolites (Family Anisograptidae) are described and revised from several heterofacial facies sections of the Broom Point Formation, Cow Head Group, western Newfoundland (Broom Point North and St Paul's represent medial to upper continental slope, Martin Point and Green Point distal slope environments). Noting potential conodont recycling in the palaeoslope environments of the proximal Cow Head Group sections, graptolites are the only group of fossils that could not have been subject to post-burial transport. The graptolites belong to an informal group of quadriradiate form-species principally representing two originally related but then diverging phyletic groups: pendent Rhabdinopora Eichwald, 1855 and horizontal to sub-horizontal Staurograptus Emmons, 1855; both being stratigraphically within Assemblage Zone I (emended after Cooper, 1979) of earliest Tremadoc or early Ibexian age (top of Cordylodus intermedius to base of C. lindstromi conodont zones). Assemblage I graptolites offer a higher resolution than coeval conodonts and are a better tool for inter-facies correlations both within the Broom Point Formation and with other graptolitic sequences on a global scale. Form-species of quadriradiate Rhabdinopora rustica (such as ?R. praeparabola and R. parabola) and of Staurograptus dichotomus (e.g. ‘Radiograptus’ or ‘Heterograptus’ flexibilis or ‘Aletograptus’) are interpreted as astogenetic morphs, or as phylogenetically descendant variants of these forms. Upon evidence of late astogenetic insertion of dissepiments in Staurograptus and Anisograptus the names ‘Heterograptus’ and ‘Radiograptus’ are placed into junior synonymy, and ‘Aletograptus’ is regarded a junior synonym of Staurograptus because its post-primary dichotomies are merely delayed distally (or omitted) to be observed exclusively in very mature specimens. The Cow Head Group fauna is compared with earliest nematophorids from Oslo, Norway (Naersnes) and Dayangcha, Jilin, China (Xiaoyangqiao), and a new comprehensive ecostratigraphic zonation for early Tremadoc graptolites is proposed.
Techniques for quantitative stratigraphic correlation: a review and annotated bibliography
Authors: Tipper J. C. 
Published: May 2009

AbstractThe development of techniques for quantitative stratigraphic correlation has tended to outstrip their acceptance by practising stratigraphers. To make these techniques more readily accessible and to encourage their use, this paper presents a brief, general review of the problem of quantitative stratigraphic correlation and then shows how, using a natural framework for stratigraphic correlation, the stratigraphic time-series, there can be seen an orderly pattern among them. The annotated bibliography, of almost 400 articles, includes a majority of those references concerned with quantitative stratigraphic correlation, in whatever sense: the scheme of annotation provides a straightforward, albeit subjective indication of the general thrust of each article.