bluuebunny/crossref_metadata_2025_split huggingface dataset:
A complete arc-trench system recognized in Gondwana sequences of the Antarctic Peninsula region
Authors: Smellie J. L. 
Published: May 2009

SummaryPrior to Late Triassic–Early Jurassic times, the geological history of the Antarctic Peninsula region was dominated almost entirely by Gondwana sequences that together comprised a major arc-trench system. Subduction complex, trench-slope-break and fore-arc basin sedimentation can all be recognized, and deposition was at least partly on early Palaeozoic or older continental crust. The only evidence for a contemporaneous magmatic arc situated in the Antarctic Peninsula at this time consists of patchy occurrences of metavolcanic rocks, possibly representing the frontal edge of the arc, and the major outcrop area of these rocks is believed to lie under the broad shallow continental shelf E of the Antarctic Peninsula. This is contrary to most current hypotheses in which a marginal basin, presumably floored by oceanic crust, is thought to crop out close to the E coast of the Antarctic Peninsula. However, the complete absence of substantial outcrops of pre-Jurassic volcanic rocks anywhere in eastern Antarctica and South Africa, which are the closest and most likely places in which these should exist, supports the new proposal. Moreover, the identification of back-arc elements of the arc-trench system (foreland fold-thrust belt and retro-arc foreland basin) in eastern Antarctica and South Africa greatly strengthens the likelihood of the arc cropping out in the area suggested.Towards the end of the Triassic and during the Early Jurassic Periods, an intense diastrophic event, or culmination of events, of orogenic magnitude occurred (Gondwanian orogeny), causing substantial redistribution of the pre-existing elements of the arc-trench system. In particular, all the fore-arc sequences were strongly deformed, some possibly for the first time (e.g. in the fore-arc basin), and became firmly accreted to the continental margin. Moreover, the magmatic foci migrated trenchwards to intrude the deformed rocks in the Antarctic Peninsula. Because many of the plutons were emplaced synkinematically, they often closely resemble ‘basement’ gneisses. The distinction between these rocks remains a serious problem in the Antarctic Peninsula and it can be solved only partially by radiometric dating.
Low grade and very low grade regional metabasic Ordovician rocks of Llŷn and Snowdonia, Gwynedd, North Wales
Authors: Roberts B. 
Published: May 2009

SummaryMetabasic assemblages belong to the prehnite-pumpellyite and greenschist facies. The isograds pumpellyite-in, pumpellyite-out/clinozoisite-in and biotite-in have been mapped, and divide the area into four metamorphic zones. Field and petrographic evidence indicate that the metamorphic crystallization was largely syn-and immediately post-tectonic, viz. end-Silurian to Devonian. The use of published Schreinemakers' bundles indicates that most of the prehnite-pumpellyite-bearing assemblages formed at high grades within the facies and that the greenschist facies rocks crystallized in the higher pressure field. As the amount of calcite increases so diagnostic Ca–Al silicates are reduced and eventually eliminated from assemblages. Contrary to recent claims, the evidence indicates that the Gwna Group and the Gwyddel Felsitic Beds of Llŷn were metamorphosed prior to the Arenig.
Microfabric, mineralogy and early diagenetic history of the Whitby Mudstone Formation (Toarcian), Cleveland Basin, U.K.
Authors: Pye K. , Krinsley D. H. 
Published: May 2009

AbstractThe Whitby Mudstone Formation in northeast England contains three shale facies (normal, restricted and bituminous) which have previously been differentiated on the basis of sedimentary structures and faunal assemblages. This paper shows that the three facies can also be differentiated by mineralogical, geochemical and microtextural criteria determined using BSEM, EDXRA, XRD and XRF. The bituminous shale facies consists of finely laminated shales containing an early diagenetic mineral assemblage dominated by pyrite, calcite and dolomite. The weakly laminated restricted facies shales contain an early diagenetic assemblage dominated by pyrite. The normal facies shales are very weakly laminated and contain siderite in addition to pyrite. The geochemical conditions which left a dominant early diagenetic imprint on the three facies are interpreted to be carbon-rich sulphidic, carbon-poor sulphidic and very carbon-poor sulphidic respectively.
Thermal structure of crystallizing magma with two-phase Convection
Authors: Morse Stearns A. 
Published: May 2009

AbstractTwo-phase packets of crystals plus liquid form rapidly at a magma contact having a high thermal contrast with its surroundings. The packets can detach from an upper contact and settle rapidly with respect to crystal settling or turbulent stirring velocities. They carry crystals and supercooling downward and act as heat sinks for crystallization of floor cumulates. Evolution of picritic magma toward neutral buoyancy and overturn into overlying basalt magma proceeds most efficiently with two-phase convection. Sinking of hot bronzite-laden liquid into cooler anorthositic liquid destroys the liquid stratification within a day or so. Two-phase convection rarely yields crystal mush thicknesses suitable for compaction of cumulates, which occurs only for a narrow window of cooling rates. Two-phase convection leads to cool, thin boundary layers above and below hot interior magma and may tend to prevent or control turbulence. The critical timing and scale of two-phase layer detachment need further study.
Lower Palaeozoic stratigraphy in the southern and central Amanos Mountains, south central Turkey
Authors: Dean W. T. , Monod O. , Günay Yilmaz 
Published: May 2009

AbstractFormations of Cambrian and Ordovician age originally identified by the letters A to E in the southern Amanos Mountains are reviewed using lithostratigraphic units known from the western Taurus Mountains and south-eastern Turkey. The youngest Cambrian rocks in the southern Amanos belong to the Sosink Formation and their age, based on trilobite evidence, ranges from theBadulesiaZone to theSolenopleuropsisZone of the Middle Cambrian; they are overlain unconformably by conglomerates dated as Triassic? by means of plant fossils. Ordovician rocks – Seydişehir Formation (approx. Arenig) and Bedinan Formation (Caradoc in part) – are exposed further north, in the central Amanos. The unusual position of the allochthonous ophiolites, which rest in part directly upon Lower Palaeozoic rocks, is discussed.
The Newer Granite problem: a geotectonic view
Authors: Soper N. J. 
Published: May 2009

AbstractThe Siluro–Devonian suite of granitic plutons in the British Caledonides known as the Newer Granites, together with their associated extrusive rocks, represent one of the most extensively researched examples of calc-alkaline magmatism apparently related to orogeny. Although recent chemical studies have credibly interpreted some of the Scottish intrusions and volcanic rocks as part of a continental-margin magmatic arc generated by the subduction of lapetus oceanic lithosphere beneath Laurentia, insurmountable problems of distribution and timing arise when attempts are made to relate the magmatic activity as a whole to a traditional two-plate collision model for the orogeny.Newer Granite magmatism is here discussed in the context of more mobilistic models for the post-Grampian evolution of the British Caledonides which involve E–W closure between Laurentia and Baltica, terminated by collision in the Silurian, followed by the northward accretion of Gondwana-derived terranes in the early Devonian. The former produced the Main Caledonian tectonometamorphism of the Northern Highlands of Scotland, the latter the Late Caledonian deformation of the slate belts in the paratectonic Caledonides. These models imply much more complex convergence geometries which can, in principle, account for the whole Newer Granite suite as a series of subduction-generated magmatic arcs overlapping in space and time.The model proposed involves three late Caledonian magmatic arcs in addition to the Ordovician ‘Borrowdale arc’ which is not considered in this paper. One is related to Laurentia–Baltica convergence with westward subduction beneath the Scottish sector of the Laurentian margin in the Ordovician and Early Silurian, which generated the early members of the Newer Granite suite in the Highlands; a second is related to northward Silurian–early Devonian subduction at the Solway Line, which generated the younger Newer Granites and volcanic rocks north of the Highland Border; and a third, related to northward accretion of the Armorican terrane in early Devonian time, produced intrusive and extrusive magmatism as far south as Southeast Ireland and the English Midlands.
The succession of small shelly fossils (especially conoidal microfossils) from English Precambrian–Cambrian boundary beds
Authors: Brasier Martin D. 
Published: May 2009

AbstractSmall shelly fossils, especially conoidal microfossils, have potential for biostratigraphic correlation of Precambrian–Cambrian boundary rocks where evolutionary successions of taxa can be recognized. A succession of hyoliths, brachiopods and species of Sunnaginia, Torellella, Eccentrotheca and Rhombocorniculum can be recognized in the Home Farm Member of Nuneaton and/or the Comley Limestone of Shropshire, England. Revised ranges of taxa are given and Sunnaginia neoimbricata n.sp., S. parva n.sp., S. angulata n.sp., Eccentrotheca grandis n.sp. and several new records are described from Nuneaton and Comley. The similarity in the sequence of small shelly fossils in England and Siberia indicates that a correlation can be achieved between the two areas. It is suggested that the lower Tommotian to lower Atdabanian correlates with the Hartshill Formation of Nuneaton, of which the condensed Home Farm Member spans the mid Tommotian to lowest Atdabanian, while the upper Atdabanian to lower Botomian correlates with the condensed Comley Limestone of Shropshire.
Petrography of trench sands from the Nankai Trough, southwest Japan: implications for long-distance turbidite transportation
Authors: De Rosa R. , Zuffa G. G. , Taira A. , Leggett J. K. 
Published: May 2009

AbstractTwenty-three samples of Quaternary sands from Deep Sea Drilling Project (DSDP) Leg 87 Sites 582 (trench axis) and 583 (lowermost terrace of uplifted trench sediments in the accretionary prism) off Shikoku show a 70–80% volcanic component in the terrigenous grain population. This component comprises 30–40% neovolcanic grains, among which basic and intermediate types are present in roughly equal proportions, and 60–70% palaeovolcanic grains, which are predominantly of acidic composition. No volcanic terrane occurs, in the hinterland of the Shikoku portion of the Nankai Trough, and the first such rocks to the east (up the very slight depositional slope of the Nankai Trough axis) are not encountered for more than 500 km. These, occupying the Izu Peninsula and the majority of the Tokai drainage basin to the north, are Neogene and Recent volcanics which are of comparable variability to the volcanic grains in the sands off Shikoku.The minor component of sedimentary, metamorphic and plutonic grains in the Leg 87 sand samples can be matched with the basinal clastic ophiolitic Shimanto and Chichibu terranes and the high-pressure metamorphic Sambagawa terrane which border the Nankai Trough fore-arc along southwest Japan. This detritus also most likely derives from the Tokai drainage basin, where the easternmost outcrops of the above-mentioned terranes occur, because most sediments deriving from Shikoku and the Kii regions are ponded in terraced fore-arc basins or in basins on the lower slope. Only three major submarine canyons debouch into the floor of the Nankai Trough. The easternmost of these, the Suruga Trough, taps the volcanic Izu/Tokai hinterland, and is therefore the conduit for most sand fed to the trench off Shikoku.
An early Late Cambrian trilobite faunule from Kashmir
Authors: Jell P. A. 
Published: May 2009

AbstractAn early Late Cambrian trilobite faunule of fewer than 20 specimens and includingMonkaspissp. cf.M. serrataMong, ?Blackwelderiasp. andCyclolorenzellasp. is recorded from the Trahagam Formation near the village of Trahagam in Hundwara Tehsil, Kashmir, India. The faunule occurs in green shales and provides the first unequivocal Late Cambrian date for sediments in Kashmir; Kashmiri fossil faunas previously ascribed Late Cambrian ages by Reed are now considered Middle Cambrian.
On the thermo-tectonic evolution of Northern England: evidence from fission track analysis
Authors: Green Paul F. 
Published: May 2009

AbstractThe limited amount of fission track data previously available in Northern Britain has shown unexplained Cretaceous ages in the Southern Uplands and Lake District. Apatite fission track analysis has been applied to 23 samples from Caledonian intrusive bodies, to further investigate these ages. Fission track data of sphene has been carried out on seven samples and zircon in one sample.Apatite fission track ages vary from a maximum of 278 ± 12 Ma in the Cheviot Granite, down to ages of ∼ 60 Ma in the Carrock Fell region, with intermediate ages of ∼ 140 Ma in the Eskdale Granite and ∼ 80 Ma in the Shap Granite. This variation in fission track age is accompanied by changes in the distribution of confined fission track lengths. Samples with the youngest ages (∼ 60 Ma) have long, narrow distributions (mean length > 14 μm; standard deviation ∼ 1 μm) typical of samples which have had all pre-existing tracks erased by elevated temperatures, and subsequently cooled rapidly so that all tracks now observed have formed at low temperatures. As ages increased from 60 Ma, a component of shorter tracks becomes more dominant, representing tracks which have been shortened at elevated temperatures. Thus ages greater than 60 Ma are ‘apparent ages’, representing a partial overprint of a pre-existing track record, while the ∼ 60 Ma ages record a total resetting at this time.The heating responsible for the observed fission track annealing may be due to residence at temperatures in the range 70–125 °C over many tens of Ma, or to a short lived heat pulse perhaps associated with the Tertiary igneous province of the northwest. In either case, uplift and erosion on a scale of kilometres at ∼ 60 Ma ago is necessary to produce the observed pattern of fission track parameters. This uplift may be related in some way to basin inversions, also on a kilometre scale, known to have taken place at around the Late Cretaceous/Early Tertiary to the southeast (Cleveland, Sole Pit and Broad Fourteens Basins). No previous evidence of such uplift in Northern England has been reported, and the study reported here highlights the unique potential of apatite fission track analysis for the detection of mild thermo-tectonic events, often in areas where no other evidence exists.
Observations onAstiericeras astierianum(d'Orbigny, 1842) (Cretaceous Ammonoidea)
Authors: Kennedy W. J. 
Published: May 2009

AbstractAstiericeras astierianum(d'orbigny, 1842) is redescribed, the type material illustrated for the first time and the range of intraspecific variation and striking sexualdimorphism documented. Previous suggestions that the early ontogeny ofAstiericerassupports derivation fromDouvilleicerasde Grossouvre, 1894 of the Douvilleiceratinae are in error: the genus and species are distinctive at the earliest diameters seen and ornament gives no clue to affinities. The sutural formula is that characteristic of some Douvilleicerataceae, however, to which superfamily the species is assigned, as the only member of the family Astiericeratidae Breistroffer, 1953. It is thus a scaphitoid heteromorph, derived from normally coiled immediate ancestors that are themselves recoiled derivatives of an original heteromorphic stock.
Fossil plants of the Severn Coalfield and their biostratigraphical significance
Authors: Cleal C. J. 
Published: May 2009

AbstractThe Carboniferous fossil plants from the Severn Coalfield are described for the first time. They indicate a late Westphalian D age for these strata (Lobatopteris vestitaBiozone) and are clearly similar to floras reported from the Forest of Dean Coalfield. There is also evidence that they can be correlated with the Grovesend Beds in the eastern part of the South Wales Coalfield. It seems that the start of sedimentation in the Forest of Dean and Severn coalfields is related to Leonian (late Hercynian) earth movements.
The Lower Eastern Layered Series of Rhum
Authors: Faithfull John W. 
Published: May 2009

AbstractThe Lower Eastern Layered Series (LELS) comprises approximately units 1–5 of previous workers. Remapping has revealed considerable along-strike lithological variation in the units of the LELS. It is suggested, on the basis of field and geochemical evidence, that two layers formerly regarded as ‘conformable intrusive sheets of fine-grained olivine gabbro’, may be evolved alii valite layers rather than later intrusions. Xenolith suites, in these layers and elsewhere, indicate a component derived from the roof or walls of the magma chamber. Cryptic variation is more extensive in the LELS than in other parts of Rhum: olivine forsterite content varies from 85.6 to 70, and clinopyroxene Mg×100/(Mg+Fe) varies from 88 to 74. Postcumulus effects and subsolidus re-equilibration have altered the initial compositions of the mineral phases. The data are consistent with a model of repeated replenishment by picritic magma, although the replenishing liquids may have been slightly less magnesian than those subsequently available, during the formation of the upper ELS.
Fluid dynamic and geochemical evolution of cyclic unit 10, Rhum, Eastern Layered Series
Authors: Tait Stephen R. 
Published: May 2009

AbstractLithological, major element, trace element and Sr isotope data from cyclic unit 10 of the Rhum Eastern Layered Series are presented. The lower 65 metres of the unit are peridotite, subdivided on textural and geochemical grounds into a lower homogeneous portion approximately 50 metres thick and an upper heterogeneous portion approximately 15 metres thick. The uppermost 16.5 metres of the unit are allivalite. There are steep geochemical gradients across the peridotite-allivalite boundary in Ni content of olivine and whole-rock Sr isotope composition.Calculations are presented on the geochemical evolution of a Rhum picritic liquid undergoing olivine precipitation, both when the olivines remain suspended in the residual liquid as they precipitate, and when they are continuously fractionated. Quenched groundmass and olivine compositions from the Rhum dykes and the unit 10 peridotite olivines show good agreement with the suspension model but are inconsistent with the fractionation model. The Rhum chamber is thought to have been replenished with a picritic liquid from which olivine crystallized while held in suspension; however, replenishment by a highly olivine-phyric basalt is also possible. The peridotite probably accumulated rapidly as olivines were dumped out of suspension onto the chamber floor.The lower part of the peridotite is a poikilitic adcumulate; it is suggested that this formed by convective circulation of melt in the pores of the pile of cumulus olivines. In the latter stages of adcumulus growth, more Fe-rich and isotopically contaminated magma entered the top of the cumulus pile causing cumulus olivines to re-equilibrate and giving the intercumulus plagioclase a higher Sr isotope ratio than lower down. The olivines in the allivalite show steep stratigraphic gradients in major element composition but not in their Ni content. They also show substantial variation in major element composition laterally within the allivalite. It is suggested that these features are a consequence of postcumulus re-equilibration of olivine with migrating intercumulus magma.
Channelled metasomatism in Rhum layered cumulates – evidence from late-stage veins
Authors: Butcher Alan R. 
Published: May 2009

AbstractLate-stage veins have been studied in the Rhum layered intrusion as part of a wider investigation into postcumulus processes – in particular, to study compositions of residual liquids and their effects on host cumulates. Studies have concentrated on Unit 10 of the Eastern Layered Series (ELS), though brief investigations have also been made in the Western Layered Series (WLS).The Unit 10 veins are generally concordant with the layering, although locally they are transgressive with dilational relationships. Two principal types can be recognized: ultrabasic and basic. Detailed microprobe studies have shown that the liquids responsible for the veins have substantially modified the compositions of the cumulus minerals in the wall-rock peridotite up to 1 cm from the vein margin.The style of veining in the WLS is more complex than in the ELS, and several generations of vein can be identified. Both normal and harrisitic cumulates have undergone localized chemical modification near to the veins. Modification occurs regardless of the vein orientation.The ELS and WLS veins are geochemically distinct from the numerous gabbro intrusions associated with the layered series, and it is concluded that they represent fractionated intercumulus liquids injected into early formed fractures in the cumulates. The observed chemical modification is explained by a model involving mixing of the intrusive vein melt with trapped intercumulus melt in the adjacent peridotite, followed by diffusion-controlled re-equilibration of the cumulus minerals. This type of highly localized compositional modification along fractures is termed channelled metasomatism.
Marine incursion in Upper Palaeozoic sedimentary rocks of the Oslo Region, Southern Norway
Authors: Olaussen S. 
Published: May 2009

SummaryThe discovery of marine fossils in the Upper Palaeozoic of the Oslo Region suggests a previously unknown marine transgression of probable middle Carboniferous age. The fossiliferous sequence in the Oslo district was probably deposited in a very shallow marine environment as indicated by its fauna, ooids and the strong micritization of the fossils. The discovery of this sequence is consistent with the rift model for the Oslo Rift Zone, and suggests a connection with the Variscan Ocean.
The Pleistocene rocks of the Cayman Islands
Authors: Brunt M. A. , Giglioli M. E. C. , Mather J. D. , Piper D. J. W. , Richards H. G. 
Published: May 2009

SummaryIn the Cayman Islands a core of Miocene and Oligocene crystalline limestones is overlain unconformably by limestones of the Pleistocene Ironshore Formation. Within this Formation five separate depositional environments are recognized. A reef facies contains corals still in their growth position. This reef facies is succeeded by a back reef facies, followed by a lagoonal facies. The lagoonal facies contains a diverse molluskan fauna of 75 species which differs considerably from that found in the present lagoons around the island. Rocks of these facies are overlain in places by ridges of calcarenite, considered to be shoal deposits. Higher ridges which overlie the Tertiary limestones and reef facies rocks are interpreted as beach ridges. It is thought that the Pleistocene sediments were deposited around a gradually subsiding core of Tertiary rocks.