bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental study of interaction between hydrous granite melt and amphibolite
Authors: Rutter Michael J. , Wyllie Peter J. 
Published: May 2009

AbstractWe have investigated the reaction between crystalline amphibolite and hydrous granite melt in static experiments at 810 °C and 1.5 kbar. Boundary layer concentration gradients in quenched silicate glass for the major element oxides and the volatile components, water and carbon dioxide, were measured using electron probe analysis and Fourier Transform Infrared Spectroscopy, respectively. We found a measurable change in the concentration of all components adjacent to the amphibolite in experiments of 66 and 330 hours duration. After I hour there was no detectable change in the concentration of major element oxides in the granitic glass, but steep concentration profiles were determined for carbon dioxide and water. A bubble-free zone developed adjacent to the amphibolite in the 66 hour experiment, and this zone increased in width after 330 hours. Reaction is controlled by dissolution of amphibolite and by transport of dissolved material through the granite melt. The rate-controlling process is chemical diffusion in the melt phase. Results confirm that in the absence of convective heat transfer and/or mechanical disaggregation of mafic inclusions, assimilation of mafic rocks by granite melt is very slow, corresponding to on the order of 10 mm for SiO2 in 1000 years.
Isotopic U–Pb ages of zircon and monazite from the Leinster Granite, southeast Ireland
Authors: O'Connor P. J. , Aftalion M. , Kennan P. S. 
Published: May 2009

AbstractA more precise age for the synkinematic emplacement of the large S-type Leinster batholith (southeast Ireland) has been obtained by U–Pb dating of zircon and monazite separates from the two main granite varieties of the Northern Pluton. A concordant age of 405±2 Ma derived from monazite is considered to reflect both the age of intrusion and the main regional deformation event (D1) in southeast Ireland. The monazite age is in good agreement with an earlier, less precise whole-rock Rb–Sr isochron determination. The zircon data indicate recent Pb loss effects and the existence of a small component of inherited radiogenic Pb derived from a crustal precursor during the generation of the batholith.
Radiocarbon dating and sedimentation rates in the Holocene alluvial sediments of the northern Bihar plains, India
Authors: Sinha Rajiv , Friend Peter F. , Switsur V. R. 
Published: May 2009

AbstractSeven radiocarbon dates of carbonate shells and charcoal from the upper two metres of sediment in the Indo-Gangetic plains of northern Bihar, eastern India, can be divided into three groups, with the following approximate ages: 2400±45 a BP (two samples), 1100±45 a BP (four samples) and 765±45 a BP (one sample). This evidence for at least three episodes of sedimentation in the last 2400 a contrasts with evidence of greater ages from similarly near-surface sediments in the middle Gangetic plains of Uttar Pradesh, further west. In these more westerly areas, greater ages and well-developed river terraces point to much more restricted late Holocene sedimentation. Rates of net sediment accumulation calculated using our Bihar ages, spanning a period of the order of 103–104a, are similar to those calculated for periods of the order of 105–106a for the Himalayan foreland basin. This suggests that, in the whole basin case, short-period rates higher than the Bihar rates have been compensated by longer than Bihar periods of non-deposition or erosion.
The role of the Secondary Standard in stratigraphy
Authors: Cope J. C. W. 
Published: May 2009

AbstractThe development of a series of internationally acceptable chronostratigraphical units initially grew up through agreed use. Today's requirement of endorsement by the International Commission on Stratigraphy has resulted in the official rejection of names which are perfectly valid and still essential in the parts of the world for which they were introduced. Recognition of this fact is urged, by the acceptance of the Secondary Standards as locally defined chronostratigraphical units pending possible future correlation with the primary standard.
First Permo-Carboniferous conodonts from North Greenland
Authors: Rasmussen Jan Audun , Håkansson Eckart 
Published: May 2009

AbstractUpper Palaeozoic conodonts are described for the first time from the North Greenland Wandel Sea Basin. In eastern Peary Land, the Moscovian speciesIdiognathodus incurvusand the Kasimovian—GzhelianI. magnificusoccur in the Upper Carboniferous Foldedal Formation, while an assemblage from the lower part of the succeeding Kim Fjelde Formation suggests deposition in the Upper ArtinskianNeostreptognathodus pequopensis—N.clarkiZone. These datings confirm the existence in the northern part of the Wandel Sea Basin of the pronounced early Permian hiatus previously recognized in Holm Land and Amdrup Land in the southern part of the basin. The single conodont specimen found at Prinsesse Ingeborg Halvø further corrobates the local absence of this regional hiatus in the central part of the Wandel Sea Basin.
Intrusion age of Pan-African augen gneisses in the southern Menderes Massif and the age of cooling after Alpine ductile extensional deformation
Authors: Hetzel R. , Reischmann T. 
Published: May 2009

AbstractPb–Pb single zircon ages of 546.2 ± 1.2 Ma demonstrate that the augen gneisses in the southern Menderes Massif were generated from Pan-African intrusions. During the Alpine orogenic evolution of the Menderes Massif these granites were metamorphosed and transformed into augen gneiss in an extensional top-to-the-south shear zone, located between augen gneisses and overlying schists. Quartz fabrics suggest a pronounced static recrystallization that post-dates the ductile deformation in the shear zone. Ar–Ar muscovite ages of 43–37 Ma from augen gneisses and schists suggest that ductile deformation and subsequent cooling occurred in the Eocene. These results contradict previous models that (1) interpret the extensional shear zone as late Oligocene in age and (2) regard the augen gneisses as syntectonic with respect to ductile extensional deformation.
Excess argon in amphiboles linked to greenschist facies alteration in the Kamila Amphibolite Belt, Kohistan island arc system, northern Pakistan: insights from 40Ar/39Ar step-heating and acid leaching experiments
Authors: Wartho Jo Anne , Rex David C. , Guise Philip G. 
Published: May 2009

AbstractA mineralogical and 4OAr/39Ar study of 13 amphibole samples in the Kamila Amphibolite Belt and Kamila Shear Zone in northern Pakistan has found a correlation between the degree of greenschist facies alteration and quantity of excess 40Ar. Additionally, there is a north–south divide with amphibole samples from the northern region showing larger degrees of gree schist facies alteration, brittle deformation, and excess 40Ar incorporation compared to the predominantly plastically deformed, less altered, amphibole samples from the Kamila Shear Zone in the south. Acid leaching of two amphiboles from the Kamila Amphibolite Belt indicates that a large proportion of the excess 40Ar is correlated with later greenschist facies alteration hases, and can be easily removed by acid etching, thus revealing acceptable regional 40Ar/39Ar plateau ages.
Phytoplankton from the Lower Cambrian Læså formation on Bornholm, Denmark: biostratigraphy and palaeoenvironmental constraints
Authors: Moczydłowska Małgorzata , Vidal Gonzalo 
Published: May 2009

AbstractAcritarchs from the Lower Cambrian Læsså formation on Bornholm, Denmark, are taxonomically diverse. Their state of preservation, including thermal, mechanical and chemical alteration, is discussed. Different states of thermal maturation of acritarchs in shales and phosphorites of the Broens Odde member could be explained in terms of possible irradiation from natural radioactive decay. The microfossils form two age-diagnostic assemblages that allow recognition of theSkiagia ornata–Fimbriaglomerella membranaceaandHeliosphaeridium dissimilare–Skiagia ciliosaAssemblage Zones within the Broens Odde member of the Laeså formation. Acritarch-based biostratigraphy indicates that the Lower Cambrian Balka Formation and Læså formation correspond to theSchmidliellus mickwitziZone andHolmia kjerulfiAssemblage Zone recognized in Baltoscandia and the East European Platform. Acritarch distribution within three different depositional settings indicates that comparable spectra of morphotypes occurred in different depositional environments. This suggests the absence of facies control. During early Cambrian times palaeoenvironmental barriers in shallow, epicontinental shelf basins constituted a minor obstacle for widespread distribution of acritarch taxa. Formerly proposed early Palaeozoic acritarch provincialism appears insufficiently documented in the fossil record and no evidence could be extracted from the Cambrian record. Following a rapid radiation at the onset of the Phanerozoic, Cambrian phytoplankton populations underwent dispersion following oxygenic and nutrient-rich bodies of water within epicontinental and presumably basinal environments. Lower Cambrian acritarch taxa were largely cosmopolitan and little affected by lithofacies associations. A continuous flow of data is contributing to the emergence of acritarch-based biostratigraphy. Its apparent consistency suggests great usefulness for interregional and detailed event correlation.
Climatic and oceanographic isotopic signals from the carbonate rock record and their preservation
Authors: Marshall James D. 
Published: May 2009

AbstractStable isotopic data from marine limestones and their constituent fossils and marine cements can provide quantitative evidence for changes in global climate and ocean circulation. Oxygen isotopic data can indicate changes in temperature and ocean composition whereas stratigraphic variation in carbon isotope ratios may reflect changes in the carbon cycle that can be linked to changes in oceanic productivity and atmospheric greenhouse gases. Terrestrial carbonates–meteoric cements, calcretes and speleothems–similarly offer significant potential for understanding the evolution of terrestrial climates by providing evidence for the composition of rainwater and the nature of vegetative cover.Primary environmental isotopic signals may be obscured by the effects of post-depositional diagenetic alteration. Cementation and replacement reactions can take place in a wide range of diagenetic environments; the diagenetic history of an individual limestone is determined by a combination of its mineralogical diagenetic potential and depositional setting, together with subsequent changes in relative sea-level and burial history. Carbon isotopic values are less prone to alteration during diagenesis than oxygen values but shifts can be significant where organogenic carbon is incorporated. Linear covariation of carbon and oxygen values is not a reliable indicator of diagenetic alteration: water-rock interaction and fluid mixing may produce non-linear distributions.Attempts to determine long-term changes in climatic and oceanographie conditions through isotope stratigraphy of shallow-water limestones must include an assessment of the diagenetic history of the materials analysed. Pétrographic examination using conventional microscopy backed up, where appropriate, by cathodoluminescence and scanning electron microscopy together with elemental and strontium isotopic analysis can help to identify the effects of diagenetic alteration. Where material with a range of different degrees of alteration is preserved in the same sediment it may be possible to compare patterns of isotopic and elemental variation and to attempt to unravel the effects of diagenesis in order to determine primary, environmental, isotopic signals. Recent research has shown that these techniques can be successfully employed in both Phanerozoic and Precambrian sediments.
A review of terrestrial and marine climates in the Cretaceous with implications for modelling the ‘Greenhouse Earth’
Authors: Spicer Robert A. , Corfield Richard M. 
Published: May 2009

AbstractFrom the unique perspective of the geological record, it appears that the ‘Greenhouse Earth’ was a feature of climate for up to 80 % of the last 500 Ma, and that therefore our present glacially dominated climate is an anomaly. The Cretaceous in particular was a time of global warmth, an extreme greenhouse world apparently warmer than our current Earth. The geological record provides perspective and constraints against which the success of climate models can be evaluated. At present there are no ways of evaluating model predictions for the future of our ‘Greenhouse Earth’ until after the event. Retrodicting the past is therefore a very useful way of testing model sensitivity and robustness. The geological record tells us that the characteristics of the Cretaceous greenhouse world were a shallower equator-to-pole temperature gradient, shallow, well-stratified epicontinental seas with a tendency towards periodic dysaerobism, and a well-developed terrestrial flora extending to the high latitudes. Both marine and non-marine data show a global cooling trend throughout Late Cretaceous time, a trend that seems to correlate with declining atmospheric carbon dioxide.
Ediacaran fossils from the Innerelv Member (late Proterozoic) of the Tanafjorden area, northeastern Finnmark
Authors: Farmer J. , Vidal G. , Moczydłowska M. , Strauss H. , Ahlberg P. , Siedlecka A. 
Published: May 2009

AbstractAn Ediacaran assemblage dominated by an unidentified species ofCyclomedusaSprigg 1947, along with species ofEdiacaria?Sprigg 1947,BeltanellaSprigg 1947,HiemaloraFedonkin 1982, andNimbia?Fedonkin 1980, is described for the first time from the Innerelv Member of the Stappogiedde Formation exposed in coastal outcrops west of Tanafjorden on Digermul Peninsula, in northeastern Finnmark, northern Norway. The fossil assemblage is dominated by discoidal forms which share certain affinities with the cosmopolitan genera.CyclomedusaandEdiacaria. However, our specimens differ from these and other discoidal Ediacaran fossils in the absence of radial sculpture. This, along with a basically concentric organization, are characteristics shared withKullingiafrom the Dividal Group of northern Scandinavia, the White Sea, Podolia, and northwestern Canada, along with undescribed discoidal remains from the Charnian Supergroup, Charnwood Forest, Leicestershire, England, and the Conception Group, Avalon Peninsula, Newfoundland.Our discovery of an Ediacaran-type assemblage within the Middle Innerelv Member provides support for previous suggestions of a late Vendian age for this sequence. This general conclusion is consistent with the occurrence of early Cambrian taxa, including the trace fossilPhycodes, and the problematical formsVendotaeniaandSabellidites,in basal portions of the Lower Breivik Formation, within the same stratigraphie section. The lowest formally-proposed faunal zone in northern Scandinavia is theKullingiaZone, based on the occurrence of the fossil medusoidKullingia concentricain Member III (Middle Sandstone C) of the Dividal Group, northern Scandinavia.Kullingiais a distinctly chambered form that was probably pelagic. In contrast,Cyclomedusa,and related genera of the so-calledCyclomedusaplexus, comprise an informal grouping of intergrading, probably benthic, taxa that possess radial and/or concentric organization. In light of the intergradational nature of taxa, present difficulties in taxonomic interpretation and correlation, and the abundance of cyclomedusoids in many Ediacaran assemblages, we suggest that the concept of theKullingiaZone, as originally defined for northern Scandanavia, be broadened to include the common form genera of theCyclomedusaplexus, inclusive of the occurrences in the Innerelv Member described herein. It is our hope that additional fieldwork will provide a basis for more refined taxonomic evaluations and biozonation.
A combined petrographical—geochemical provenance study of the Newland Formation, Mid-Proterozoic of Montana
Authors: Schieber Jürgen 
Published: May 2009

AbstractA provenance study was conducted on the Mid-Proterozoic Newland Formation, in which petrographical features of sandstones and geochemical characteristics of shales were integrated to arrive at an internally consistent interpretation.Sandstones of the Newland Formation are typically arkosic sands and arkoses with very-well-rounded quartz and feldspar grains and only minor amounts of extrabasinal rock fragments. The predominant feldspar types are K-spar and microcline, feldspar grains are smaller than quartz grains, and feldspars show little alteration due to weathering. Detrital modes of Newland sandstones (QFL diagrams) indicate that they were derived from a stable cratonic source. These petrographical features imply a source area dominated by granites and granitoid gneisses, semi-arid to arid climate, tectonic quiescence, and overall peneplain conditions.Shales of the Newland Formation are dominated by illite, quartz silt, and fine crystalline dolomite. They have small La/Th rations, relatively large Hf contents, and small contents of Cr, Co, and Ni, all indicative of derivation from crust of granitic composition. Small Tio2/Al2O3ratios also suggest source rocks of granitic composition. The average chemical index of alteration (CIA) for Newland shales is 71.8, which in light of the probable granitoid source indicates modest amounts of chemical weathering. Relatively large SiO2contents and large K2O/Na2O ratios reflect derivation from stable cratonic areas and tectonic quiescence.Thus, in general, the petrography of sandstones and geochemistry of shales provides the same provenance clues for the Newland Formation. One notable discrepancy between the two approaches is that the sandstones indicate an arid to semi-arid climate with very minor chemical weathering, whereas the CIA of the shales indicates at least modest amounts of chemical weathering. This indicates on one hand the need to better calibrate the CIA with a large variety of muds from modern climatic settings, and on the other hand the possibility that this discrepancy is due to transport segregation.
Oxygen isotope evidence for major fluid flow along the contact zone of the Rum ultrabasic intrusion
Authors: Greenwood R. C. , Fallick A. E. , Donaldson C. H. 
Published: May 2009

AbstractRecent studies indicate that the Rum Tertiary ultrabasic intrusion formed in situ, and was not emplaced as a fault-bounded plug. The suggestion that the Main Ring Fault was the primary pathway for the flow of meteoric-hydrothermal fluids on Rum is therefore seriously flawed. Oxygen isotope evidence is presented indicating that the contact zone of the intrusion was the major pathway for meteoric fluids during cooling of the pluton. δ18O depletions of over 12‰ correlate with hydrothermal alteration assemblages, indicating that the bulk of the interaction with meteoric fluids took place at low temperatures (200–450 °C).
Two new graptolites from the early Silurian (Llandovery: Aeronian) of central Wales: an origin for monoclimacid thecal morphology
Authors: Zalasiewicz J. A. 
Published: May 2009

AbstractMonograptus chrysalissp. nov. from themagnusZone (Aeronian) of central Wales shows a previously unrecognized combination of thecal types. Distally, the thecae possess marked lappets and short lateral horns, and approximate to those of therevolutusgroup of monograptids and some described examples ofPribylograptus. Proximally, the thecae are elongate and slender, and possess slit-like apertures below a distinct geniculum. They resemble the proximal thecae ofMonograptus imagosp. nov., one of the earliest recognized British monoclimacid monograptids, from the succeedingleptothecaZone of central Wales and the Lake District. It is suggested thatM. chrysalisarose from a graptolite of therevolutusgroup by retraction or suppression of the hooked proximal thecae, while the distal thecae remained constant, and thatM. imagothen evolved fromM. chrysalisby a spreading of the proximal end characteristics distally. The proximal morphology and overall record of the monoclimacids, though, suggests that they may be polyphyletic; in this paper, the generic nameMonoclimacisis reserved for the late Telychian graptolites of thevomerinagroup.
Pliocene—Quaternary sedimentation in the Northern Apennine Foredeep and related denudation
Authors: Bartolini Carlo , Caputo Riccardo , Pieri Marco 
Published: May 2009

AbstractThe deposits of the Pliocene—Quaternary foredeep of the Northern Apennine cover at present an area of 103000 km2. The original boundaries of the basin are not known, since marginal deposits have been eroded, in particular those of the inner, southwestern border. During Pliocene times the basin area was reduced by thrust tectonics and the amount of shortening may be tentatively estimated.The present volume of Pliocene and Quaternary sediments may be inferred with good approximation from the maps of the base of the Pliocene and of the Quaternary (base of the Hyalinea balthica Zone) successions. The Pliocene volume has been corrected adding the estimate of the underthrust sediments, while no correction has been attempted for the eroded marginal deposits. The estimates of 97000 and 95000km3. reflecting the present volume of the Pliocene and Quaternary deposits, are therefore significantly less than the volumes originally deposited.Present volumes have been transformed in ‘net’ (0% porosity) volumes, in order to obtain the relative net supply rates: 0.021 (Pliocene) and 0.047 (Quaternary) km3/a. Other unmeasurable factors (volume variations due to the weathering of silicates, loss of leached carbonates) may induce a probably unimportant underestimate of the supply rates.Available data allow an approximate estimate of the range of the net volume of the Holocene sediments deposited during the last 6000 a BP (221–276km3) and of the relative net supply rate (0.037–0.046km3/a), that is not significantly different from the Quaternary one. Applying a porosity correction, these supply rates may be related to the Quaternary source area (128000km2) to obtain the relative denudation rates: 0.41–0.46mm/a (Quaternary) and 0.36–0.51 mm/a (Holocene). Present supply and denudation rates, deduced from the direct measurements of the bed load and suspended load of the apenninic and alpine rivers, do not differ significantly from the Quaternary and Holocene ones.Available data do not allow a reliable estimate of the Pliocene source area, and consequently of the Pliocene denudation rate. However, a minimum of 160000–177 000 km3 has been eroded during Pliocene and Quaternary times. Assuming, as a working hypothesis, that the Pliocene source area did not significantly differ from the present one, an average thickness of 1240–1390 m could have been eroded since the beginning of Pliocene. This estimate is in agreement with the values obtained from the measurements of coalification of vegetal organic matter in the outcrops, and suggests that post-orogenic successions and ‘higher’ thrust sheets may have been completely removed in vast areas.
Evidence for late Precambrian to early Cambrian orogeny in northwest Himalaya, Pakistan
Authors: Baig M. S. , Lawrence R. D. , Snee L. W. 
Published: May 2009

AbstractAn angular unconformity below Cambrian rocks is present in the northwest Himalaya in the Hazara district, Pakistan. Low-grade metamorphism and folding with axial planar cleavage present in Precambrian rocks below the unconformity, but not in those above it, confirm orogenic deformation at this time. This is the first clear evidence for such a deformation episode and it may be referred to locally as the Hazaran orogeny. Anatectic peraluminous granites of the Himalaya are of only slightly younger age and may be related to this orogenic episode.