bluuebunny/crossref_metadata_2025_split huggingface dataset:
The relative stratigraphic position of the foraminiferal and belemnite standards for the Campanian–Maastrichtian boundary
Authors: Hancock Jake M. , Russell Ernie E. , Taylor Richard H. , Gale Andy S. 
Published: May 2009

AbstractThe two most commonly used biostratigraphic standards for the Campanian–Maastrichtian boundary are the appearance of the belemniteBelemnella lanceolata(Schlotheim) and the disappearance of the planktic foraminiferanGlobotruncanita calcarata(Cushman). The first is a boreal standard, the second tethyan. The assumption that the two coincide is false. In Mississippi the disappearance ofG. calcaratais the same eustatic peak of sea-level which in north Germany lies near the top of theNostoceras polyplocumZone, within boreal nannofossil Zone CC/B22. This places the foraminiferal standard somewhere between 1.3 and 3.5 m.y. older than the belemnite standard. The belemnite standard is at or close to the appearance ofGansserina gansseri(Bolli) in Mississippi.
Age and significance of radiolarian sediments within basic extrusives of the marginal basin Guevgueli Ophiolite (northern Greece)
Authors: Danelian Taniel , Robertson Alastair H. F. , Dimitriadis Sarantis 
Published: May 2009

AbstractWell-preserved Radiolaria have been discovered in calcareous silt turbidites and mudstones intercalated with basic extrusives of the Guevgueli Ophiolite, northern Greece. The mudstones contain terrigenous silt, probably derived from adjacent continental basement of the Serbo-Macedonian and/or Paikon units. Volcanic quartz and rare volcanic glass were probably derived from an active continental margin arc (Paikon volcanic arc) to the west. The radiolarian sediments were deposited within fault-controlled hollows in the ophiolitic extrusives, and then covered by massive and pillowed extrusives. The radiolarian assemblage is indicative of an early Late Jurassic (Oxfordian) age, which therefore dates the genesis of the Guevgueli Ophiolite. Our data are consistent with the age of the intrusive Late Jurassic Fanos Granite, believed to be contemporaneous with the Guevgueli Ophiolite. In general, the Guevgueli and related ophiolites of northern Greece are thought to have formed within a transtensional intra-continental marginal basin, generated in response to oblique eastward subduction of older Tethyan oceanic crust (Almopias ocean).
New Rb–Sr and U–Pb ages for the Carnsore Granite and their bearing on the antiquity of the Rosslare Complex, southeastern Ireland
Authors: O'Connor P. J. , Kennan P. S. , Aftalion M. 
Published: May 2009

AbstractA 12-point whole-rock Rb–Sr isochron for the Carnsore Granite of southeastern Ireland yields an age of 428±11 Ma and initial 87Sr/86Sr ratio of 0.7068±0.0003 (index of goodness of fit, MSWD = 0.65). A similar mean 207Pb/206Pb age of 432±3 Ma from three slightly discordant zircon size fractions from the granite is also indicated, and shows that the pluton was emplaced contemporaneously with the neighbouring Saltee Granite.Thus, Tuskar Group rocks, which are intruded by the Carnsore Granite, could be as young as Ordovician. While the early history of the Rosslare Complex is undoubtedly Precambrian, the new age for the Carnsore pluton means that the later intrusive and tectonothermal events in the history of this complex are no longer constrained to be Precambrian and may have occurred over a 150 + Ma interval in Cambro-Ordovician time.The zircons from the Carnsore Granite are slightly discordant, and show no apparent inherited radiogenic lead component. The initial 87Sr/86Sr ratio suggests that the magma may have been derived as a melt in the lower crust. The higher strontium isotope ratios of the Rosslare gneisses would seem to preclude their involvement in the genesis of the Carnsore magma.
Goethite ooids: growth mechanism and sandwave transport in the Lower Greensand (early Cretaceous, southern England)
Authors: Schiavon N. 
Published: May 2009

AbstractThe Woburn Sands (Lower Greensand Group, Aptian–Albian age), in Billington Crossing quarry, Leighton Buzzard, Bedfordshire, England, show, along bedding planes of tabular cross-stratification, foreset alternations of quartz grains and goethitic ooids. Field and petrographic evidence suggest that: (a) the goethite in the layers and cores is primary; (b) the ooids formed by mechanical accretion of original Fe-hydroxide gels around nuclei on the sea-floor in shallower nearshore adjacent environments; (c) goethite cores of some ooids represent an earlier stage of iron deposition within the sediment where silica adsorbed by the iron-gels segregated in inclusions; (d) short-term variations in current strength and iron supply are responsible for the different arrangements of goethite platelets (tangential to random to radial) in the ferruginous layers in connection with the degree of crystallization of the colloidal iron during the accretion stage; (e) the ooids were then swept away in deeper waters by tidal action where their segregation in the lower parts of each foreset lamina is believed to have been hydraulically controlled.
Silicification of Permian calcareous algae from Nanjing, China
Authors: Mu Xinan , Riding Robert 
Published: May 2009

AbstractCalcareous algae in limestones of the Permian Chihsia Formation near Nanjing, China, are preferentially replaced by quartz. Replacement postdates both cementation by sparry calcite and also neomorphic alteration of the original skeletons to sparry calcite. It is thus diagenetically relatively late. The original replacement silica could have been massive opal CT, opal CT lepispheres, or quartz. Lepisphere-like bodies occur in a few specimens. Megaquartz rims represent later overgrowths on the silicified skeletons. Although the original ultrastructure of the algal skeletons is not preserved, the preferential silicification allows fine details of the skeletal morphology of the algae to be observed and the distribution of silica indicates the style of replacement which has probably occurred. In some specimens it is possible that dissolution of the skeleton was followed by void-filling by silica, including the possibility of lepisphere formation. But in other casesin situreplacement, probably by massive opal CT or quartz, is reflected by the replacement of the outer parts of calcite crystals by silica. This process produces a network of silica, and as it proceeds the calcite centres of the grains become progressively smaller until silica replacement is complete. Sponge spicules may have provided the most important silica source for replacement. It is proposed that water-insoluble organic films surrounding matrix grains, and now preserved as bituminous material, protected the matrix from replacement thus promoting selective late diagenetic silicification of these fossils.
A revision of the upper part of the Saq Formation and Hanadir Shale (lower Ordovician) of Saudi Arabia
Authors: El-Khayal A. A. , Romano M. 
Published: May 2009

AbstractThe previously termed Hanadir Shale of Saudi Arabia is described and re-defined as the Hanadir Formation. At the type locality of Al Hanadir the unit is probably entirely of Llanvirn age while further north shelly faunas of possible Llandeilo age occur in the upper part. Trace fossil assemblages with abundant cruzianids (C. furcifera, C. rugosa, C. goldfussi),Pelecypodichnus, DidymaulichnusandDiplichnitesindicate an Arenig age for beds in the upper part of the underlying Saq Formation, while the top of this unit yielded hitherto unrecorded pendent and biserial scandent graptolites, a sparse shelly fauna of lingulacean brachiopods,Neseuretussp. and the trace fossilsCruziana? imbricataandPhycodes.
New observations on a Pridoli plant assemblage from north Xinjiang, northwest China, with comments on its evolutionary and palaeogeographical significance
Authors: Chong-Yang Cai , Ya-Wei Dou , Edwards D. 
Published: May 2009

AbstractDetailed descriptions of plant remains from a late Silurian (Pridoli) locality in Xinjiang Province, northwest China are presented. They includeJunggaria spinosaDou, interpreted as identical withCooksonella sphaericaSenkevich,Salopella xingjiangensisDou, and a number of sterile axes, including one with a leafy appearance superficially resembling a lycophyte, and others of probable algal affinity. Lack of anatomical and reproductive characteristics precludes a more precise assessment of relationships. A justification for the Pridoli rather than Lower Devonian age of the assemblage is based on graptolites. The composition of the assemblage is compared with coeval ones from Europe, North America, north Africa and Kazakhstan and has closest similarities with the latter. Palaeogeographic proximity on the Kazakhstan palaeocontinent is postulated, but the dearth of global Silurian occurrences of land plants make it premature to evaluate the significance of Kazakhstan and Chinese assemblages in terms of global provincialism in the late Silurian. The most distinctive element in these assemblages (Junggaria/Cooksonella) has sporangia with more complex, indeed more enigmatic organization, than seen in most Silurian and early Devonian rhyniophytoids.
The Lower Cambrian Wrekin Quartzite and the age of its unconformity on the Ercall Granophyre
Authors: Wright A. E. , Fairchild I. J. , Moseley F. , Downie C. 
Published: May 2009

AbstractAcritarchs of Lower Cambrian age have been recovered from a clay horizon within conglomerates 6 m above the unconformity described by Cope & Gibbons (1987). The Wrekin Quartzite (34 m thick) represents beach deposits grading upwards into shelf sandstones. The stratigraphie evidence and recent age determinations suggest that although the granophyre was intruded at 560 ± 1 Ma the Cambrian Unconformity is younger than 533 ± 13 Ma.
Geological and palaeontological information and phylogenetic hypotheses
Authors: Campbell K. S. W. , Barwick R. E. 
Published: May 2009

AbstractA number of workers have accepted the proposition that phylogenetic relations between extant organisms can be determined only by reference to the characters of those organisms. Palaeontological data, it is said, have not been useful for developing or refuting such hypotheses. This view may be tested by reference to the respiratory mechanisms of dipnoans (lungfishes) and amphibians. The structure of the heart, lungs, and circulatory systems has been used by various authors to support the view that these are sister groups. Geological data derived from stratigraphy, palaeoecology, taphonomy, geochemistry and functional morphology of primitive dipnoans is used herein to show that these organisms did not engage in aerial respiration. The first unequivocal evidence that dipnoans had become air breathers is from aestivation burrows in Early Permian rocks of the U.S.A. The Dipnoi must have evolved this capacity at some time between the Early Devonian, when the group became well established, and the Early Permian. Similarities between the respiratory systems of extant dipnoans and amphibians must be the result of convergence, or of the derivation of the Amphibia directly from the Dipnoi. The latter view is not currently accepted by any workers in the field. Thus data from the fossil record are used to demonstrate the invalid use of some neontological data for the development of a phylogenetic hypothesis. Classifications of extant organisms depending on putative shared–derived morphological or physiological characters that cannot be adequately tested for convergence by reference to fossils, must be regarded with due caution.
Podiform chromitite-bearing ultrabasic rocks from the Bragança Massif, northern Portugal: fragments of island arc mantle?
Authors: Bridges J. C. , Prichard H. M. , Meireles C. A. 
Published: May 2009

AbstractThe Upper Allochthonous Thrust Complex (UATC) of the Bragança massif in northern Portugal contains a set of ultrabasic rocks interthrust with granulites. The ultrabasic rocks have refractory silicate mineral and whole rock compositions which indicate an origin as depleted mantle. Phase relationships of harzburgite samples suggest that they formed in equilibrium with high-Mg picritic melts created through a high degree of mantle partial melt extraction. Chromite in small podiform deposits has 100 Cr/(Cr + Al) ratios of 62–85, which are consistent with crystallization from such melts. Most of the chromite composition parameters are similar to those of ophiolite deposits except for the high ferric iron contents (2.77–8.95 wt% Fe2O3). Such enrichment is a feature of chromite from island arc magmas. It is suggested that the extensive partial melt extraction and chromite mineralization in the ultrabasic rocks occurred in the upper few kilometres of island arc mantle. The ultrabasic rocks were tectonically emplaced into a granulite and eclogite-bearing arc-continent collision complex during the Early Ordovician and subsequently, in the mid-Devonian emplaced over the Central-Iberian terrane.
Major northwest-directed Caledonian thrusting and folding in Precambrian rocks, northwest Mayo, Ireland
Authors: Johnston J. D. 
Published: May 2009

AbstractStructural mapping of the North West Mayo Inlier has investigated the kinematics of ductile fault and shear zones within the Dalradian and pre-Dalradian rocks. The area is characterized by an intense east to southeast trending elongation direction. Pre-Caledonian deformation is preserved as west-northwest trending sinistral mylonite zones. These are cross-cut by Grenville pegmatites and by undated mafic dykes. Subsequent deformation has been influenced by the majorbasement structures. During the Caledonian deformation, the pre-existing sinistral structures were reactivated coaxially as steep sinistral shear zones, deforming the mafic dykes. Major northwesterly verging thrusts are widespread in flat-lying zones which occur over much of the inlier. These are interpreted as D2 in age. The S2 fabric is the dominant fabric and contains an east to northeast trending mineral lineation. The southeastern part of the inlier is characterized by very large scale (wavelengths of kilometres) reclined D2 folding. This is interpreted as a crustal scale ramp zone. In the vicinity of this ramp there is evidence of earlier (F1) folds which are possibly the product of ramprelated deformation. All of these structures are interpreted as the product of northwest verging thrusting with crustal scale frontal and lateral ramps.
Age of metamorphism in the Lesser Himalaya and the Main Central Thrust zone, Garhwal India: results of illite crystallinity,40Ar–39Ar fusion and K–Ar studies
Authors: Oliver G. J. H. , Johnson M. R. W. , Fallick A. E. 
Published: May 2009

AbstractIllite crystallinity data from the Lesser Himalaya of Garhwal show that the upper Paleocene-lower Eocene Subathu Formation, deposited immediately prior to or early in the Himalayan collision, has not suffered significant regional metamorphism. The regional metamorphism in the upper Precambrian–lower Palaeozoic Lesser Himalaya must therefore be precollisional. Illite crystallinity results from Lesser Himalayan fossiliferous Permian strata show grades of metamorphism intermediate between upper Paleocene–lower Eocene and Proterozoic–lower Palaeozoic strata indicating a pre-Permian regional metamorphism for the latter.K–Ar whole rock cooling ages provide supporting evidence for pre-collisional regional metamorphism in the Lesser Himalaya. Slates and phyllites below the Main Central Thrust (MCT) show pre-Cenozoic whole rock ages, as old as Ordovician (486 Ma). Whilst resetting of K–Ar whole rock ages has occurred locally in pervasively cleaved Palaeozoic strata (near thrusts?), fracture cleaved Permian and upper Paleocene–lower Eocene sediments give whole rock ages compatible with diagenesis. The illite crystallinity results confirm that these sediments have not been heated above mica blocking temperatures.Muscovite40Ar–39Ar and K–Ar mineral ages within the 5 km thick MCT zone are as young as 8 Ma indicating that temperatures of above ~ 350°C were maintained in the MCT zone for over 10 Ma after high temperature (~ 550°C) shearing on the MCT. This heating did not affect the MCT footwall Lesser Himalaya to any regional extent, where pre-Permian low grade regional metamorphism has not been overprinted.
Regnosaurus northamptoni, a stegosaurian dinosaur from the Lower Cretaceous of southern England
Authors: Barrett Paul M. , Upchurch Paul 
Published: May 2009

AbstractThe type specimen ofRegnosaurus northamptoniMantell, a partial right mandible, is redescribed and compared with a wide variety of dinosaurian taxa. We suggest thatRegnosaurusis not an ankylosaur or a sauropod as previously thought, but represents the fragmentary remains of a ‘primitive’ stegosaur.RegnosaurusandHuayangosaurusshare two derived characters, suggesting that these two genera should be provisionally regarded as sister taxa. The implications of these findings for stegosaur evolution and biogeography are discussed briefly.
Rejuvenation of the eastern Mediterranean passive continental margin in northern and central Sinai: new data from the Themed Fault
Authors: Moustafa A. R. , Khalil M. H. 
Published: May 2009

AbstractThe Themed Fault marks the southernmost border of the Early Mesozoic passive continental margin of north Sinai. This 200-km long fault transects the northern part of the Tih Plateau that supposedly occupies a tectonically stable area. Post-Middle Eocene–pre-Early Miocene rejuvenation of this fault proceeded by right-lateral wrenching and represents a newly recognized phase of deformation in the history of north and central Sinai. The minimum estimate for the strike-slip movement on this fault is about 300–750 m. To the north of the Themed Fault is a narrow fault belt (Sinai hinge belt) that marks the boundary between a tectonically unstable crustal block to the north (the north Sinai fold belt area) and a tectonically stable crustal block to the south, the main part of the Tih plateau area.Four phases of dextral wrenching rejuvenated the faults of the Early Mesozoic passive continental margin in northern Egypt; one of them affected the Themed Fault. The oldest (Dl) deformation is early Late Senonian and is related to the closure of Neotethys and the Eastern Mediterranean basin. The D1 deformation proceeded by pure wrenching in the north Western Desert of Egypt. In contrast, it proceeded by transpression in north Sinai due to the irregular plate boundary and the relationship of this boundary to the slip vectors. D2 deformation (post-Middle Eocene–pre-Early Miocene) is clear in the Themed Fault area although reported herein for the first time; it is related to continued closure of the Eastern Mediterranean basin and proceeded by pure wrenching. D3 deformation (Late Oligocene–Early Miocene) proceeded by divergent wrenching in the north Eastern Desert and is kinematically related to the transfer of slip from the nearby faults of the Suez rift. D4 deformation (post-Early Miocene to Recent) affected the Sinai hinge belt by pure wrenching and is probably related to the left-lateral slip on the Dead Sea Transform and the related drag of the eastern edges of the fault blocks of this hinge belt. Recent seismic activity in the Sinai hinge belt perhaps indicates that the D4 deformation has continued to the present time, although morphological expression of recent tectonic movement is lacking. In contrast, the Themed Fault is seismically quiet at present.
A rock volume accumulation curve for the late Ordovician-Silurian Welsh Basin
Authors: Clayton Chris J. 
Published: May 2009

AbstractA rock accumulation curve is presented for the Ordovician-Silurian Welsh Basin, based on the volume of sediment entering the basin during each graptolite biozone. Even allowing for its inherent uncertainties, the curve still illustrates a significant and sudden increase in the rate of sedimentation in early Silurian time. This may be explained by submarine fan migration, large scale climate change, or river capture in the hinterland, but is most likely caused by tectonic uplift at source. This would support models for either an early Silurian, or late Ordovician closure of the Iapetus Ocean
Origin and environment of formation of late diagenetic dolomite in Cretaceous/Tertiary chalk, North Sea Central Graben
Authors: Maliva R. G. , Dickson J. A. D. 
Published: May 2009

AbstractDolomite is common in parts of the Chalk Group of North Sea petroleum reservoirs. The stratigraphic distribution, microtextures, and stable isotope ratios of dolomite vary both within and between four of the North Sea chalk fields examined in this study, the Eldfisk and Tor of the Norwegian Sector, the Dan Field of the Danish Sector, and the Machar Field of the United Kingdom Sector, indicating that the conditions favourable for dolomitization occurred at different times and places in the North Sea Central Graben. Dolomitization in all of the examined fields occurred late during diagenesis, after significant compactional grain breakage. Dolomite precipitation in the Eldfisk, Dan, and Machar fields occurred in modified sea water, which had Σ18O values between the assumed Cretaceous/Tertiary seawater value −1 and +8‰ (SMOW). The enrichment in 18O was probably the product of calcite recrystallization at elevated temperatures in a low water/rock ratio system. The timing of dolomitization varied with respect to organic diagenesis; dolomite precipitation in the Eldfisk Field coincided with bacterial methanogenesis whereas dolomite precipitation in the Machar Field probably coincided with bacterial sulphate reduction. The magnesium in the dolomite may have been derived from the neomorphism of high magnesium calcite to low magnesium calcite.