bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stratigraphy and geodynamics of the Mombasa Basin (Kenya) in relation to the genesis of the proto-Indian Ocean
Authors: Rais-Assa R. 
Published: May 2009

AbstractNew data obtained from the study of the Kenyan and Tanzanian coastal basins establish a rifting period at the end of the Karoo sedimentation (Upper Triassic/Lower Jurassic), in the northeastern margin of Gondwanaland. The rifting period was followed by an erosive phase and then transgression of a Tethyan sea during the Middle Jurassic. This leads to a modification of the stratigraphic succession of the region and gives new datas about the nature of separation and drifting of Gondwanaland, the genesis of the proto-Indian ocean and the paleoposition of Madagascar
Apatite fission track data from southeast Ireland: implications for post-Variscan burial history
Authors: Keeley M. L. , Lewis C. L. E. , Sevastopulo G. D. , Clayton G. , Blackmore R. 
Published: May 2009

AbstractThe results of a reconnaissance apatite fission track study from southeast Ireland are compared with modelled ages and length distributions predicted using both traditional thermal histories and the thermal history indicated by the fission track age and length data. All samples have experienced total annealing during the Variscan orogeny. There is strong evidence for significant post-Variscan, pre-Mid Jurassic heating and cooling. The modelling also recognizes a third thermal event subsequent to 100 Ma. The implications of these results are examined in terms of the timing and extent of subsidence and inversion along the northern margin of the North Celtic Sea Basin.
Conodonts from the lower Ordovician at Hunneberg, south-central Sweden
Authors: Löfgren A. 
Published: May 2009

AbstractSix sections through lower Ordovician shale and limestone at Hunneberg have been sampled for conodonts. Forty-nine limestone horizons and 34 shale surface samples yielded over 40000 conodont elements. The degree of biostratigraphic resolution permitted further subdivision of the post-TremadocParoistodus proteusZone into four successive intervals. Preliminary studies of coeval rocks in other areas of Sweden show that this subdivision applies elsewhere as well. Comparison with published sections from, for example, Newfoundland, Estonia and Kazakhstan indicates that the fourfold subdivision of theP. proteusZone proposed here could significantly increase the correlation accuracy, even internationally, within this critical part of the Ordovician. Graptolites and trilobites found together with the conodonts at Hunneberg indicated that the new subdivision could help to correlate biostratigraphic units based on these fossil groups. Thus the two lower intervals of theP. proteusZone correspond to theM. (E.) armatatrilobite Zone, and the upper two are approximately equal to theM. (V.) planilimbataZone. The base of theT. phyllograptoidesgraptolite Zone at Hunneberg lies close to the boundary between the upper middle and uppermost intervals of theP. proteusZone, but the graptolitic chronozonal boundary may be lower. The overlyingPrioniodus elegansZone is mainly represented by graptolitic shale at Hunneberg, but conodont faunas have been found in it, and co-occurrences of conodonts and graptolites have been noted.
Relative sea-level changes and the development of a Cambrian transgression
Authors: McKie T. 
Published: May 2009

AbstractThe Lower Cambrian in northwest Scotland is one example of a Lower Palaeozoic ‘orthoquartzite-carbonate’ succession deposited on a slowly subsiding, peneplained Precambrian basement during a period of relative sea-level rise. This particular setting led to the development of a very wide, low gradient shelf which was extremely sensitive to minor sea-level changes. The basal quartz arenite section (Lower Member-Pipe Rock) is a transgressive, tide-dominated systems tract, but lacks a systematic parasequence architecture because of three factors: a fluvial sediment flux was insufficient to induce shoreline progradation, accommodation space was limited during sea-level falls (which are commonly expressed by widespread erosional surfaces), and sediment yield to the shelf by transgressive reworking was a major contributor towards the preserved stratigraphy. The storm-dominated Fucoid Beds represent a condensed section and also show the effects of rapid and widespread facies belt oscillations because of the low shelf gradient. An overlying highstand systems tract is also lacking, partly due to the absence of a large fluvial sediment yield and also due to lowstand and transgressive reworking. An erosively based tidal sandsheet at the top of the Fucoid Beds, interpreted to be a lowstand systems tract, therefore rests directly on the condensed section of the underlying sequence. This was in turn reworked into linear tidal sandbanks (Salterella Grit) during slow sea-level rise, prior to the next major transgression. The limited accommodation space therefore introduced a preservational bias towards deepening-upward trends on a parasequence and sequence scale. The oscillations in facies belts, episodic subareal exposure and the potential to remove substantial portions of systems tracts suggests that Lower Palaeozoic ‘orthoquartzite’ successions may exhibit regular and abrupt vertical shifts in depositional environment which, given their subtle lithological character, may require detailed analysis to identify. Such successions may also display incomplete development of several components of transgressive-regressive sequence architecture.
Mesozoic extensional tectonics in the southeast Iberian Chain
Authors: Roca E. , Guimerà J. , Salas R. 
Published: May 2009

AbstractThe Desert de les Palmes area, in the southeast Iberian Chain, belongs to a Mesozoic NE–SW high which separated the early Cretaceous basins of the Maestrat and Aliaga-Penyagolosa from the little Orpesa basin. Its structure is characterized by the development of a system of NE–SW to ENE–WSW extensional listric faults detached in a shallow upper crustal level (1.7–2.2 km), mostly affecting the pre-Upper Cretaceous rocks. These faults record two well-differentiated rifting periods: (1) a first late Triassic–early Jurassic rifting period that divided the Desert de les Palmes high in several blocks; (2) a second early Cretaceous rifting period, only developed in the eastern margin of the Desert de les Palmes high, which was related to the opening of the Maestrat, Aliaga-Penyagolosa and Orpesa basins. Based on the comparison of the main features of this Mesozoic structure with an analysis of the structural and subsidence data already known in the neighbouring Mesozoic basins (Maestrat, Aliaga-Penyagolosa and Columbrets), a geodynamic scenario for the crustal evolution of the eastern Iberian Chain is also suggested. This involves four evolutionary stages: (1) Triassic rift (late Permian–Hettangian); (2) early and middle Jurassic postrift (Sinemurian–Oxfordian); (3) late Jurassic and early Cretaceous rift (Kimmeridgian–middle Albian), which includes a short Hauterivian postrift period; and (4) late Cretaceous postrift (late Albian–Maastrichtian).
Neoproterozoic (Vendian) ichnofossils from Lower Alcudian strata in central Spain
Authors: Vidal Gonzalo , Jensen Sören , Palacios Teodoro 
Published: May 2009

AbstractSimple trace fossils are reported from three localities in central Spain within a monotonous succession of shale and greywacke and classical turbidites attributed to the Neoproterozoic (Riphean) Lower Alcudian megaunit. The Lower Alcudian strata are believed to have a complex tectonic history including deformation during the Pan-African Orogeny. Chronostratigraphic control is not available for this structurally complex succession and fossil evidence is sparse. Here we report on a low-diversity ichnofossil association including the ichnospecies (isp.)Gordia marinaEmmons, 1844,Gordiaisp.,G.aff.arcuataKsiążkiewicz, 1977. The stratigraphically inferred Proterozoic age of the rocks, added to the present ichnofossil association, suggests that colonization of deeper waters started before the early Cambrian. We further consider that the plausible oxygen requirements of marine invertebrate(s) which produced the present ichnofossil taxa may well have exceeded the oxygen levels in a largely dysaerobic environment. A circulation model proposed by one of us (Palacios, 1989), implying the presence of extensive upwelling and descending oxygen-rich waters, helps to explain the continuous colonization of deep-water settings in Lower and Upper Alcudian strata. We argue that the ichnofaunal record of strata older than 650 Ma is both rare and inconclusive. Moreover, the present ichnofauna, being similar to ichnofaunal associations in environmentally comparable Upper Alcudian strata, is largely documented from Neoproterozoic (Vendian) and early Palaeozoic associations elsewhere. We conclude that the new ichnofossil evidence is consistent with a Vendian or younger age for the Lower Alcudian megaunit. This view is also consistent with a recently published maximum deposition age of 565 Ma inferred from U–Pb datings of detrital zircons from the supposedly much older (Middle Riphean) Tentudia Group or ‘Serie Negra’, that appears roughly time-equivalent with Lower Alcudian strata. It thus may appear that basin formation and flysch deposition in central Iberia encompass a minor segment of Neoproterozoic time, being probably limited to the Vendian. By default, formerly postulated Pan-African deformation of Neoproterozoic Lower Alcudian strata appears implausible. We further conclude that the complex pre-Phanerozoic structural history of Alcudian strata is probably restricted to Cadomian and younger deformation. Former structural models need substantial revision.
St Audrie's Bay, Somerset, England: a candidate Global Stratotype Section and Point for the base of the Jurassic System
Authors: Warrington G. , Cope J. C. W. , Ivimey-Cook H. C. 
Published: May 2009

AbstractIn 1967 the Somerset coastline near Watchet was proposed as the type area of the basal (Planorbis) chronozone of the Hettangian Stage and thus of the Jurassic System. Neither at that time nor subsequently, however, has a type locality and section been nominated from those available in the area. There is urgent need to select a Global Stratotype Section and Point (GSSP) for the base of the Hettangian, and of the Jurassic System. The cliff forming the headland at the west side of St Audrie's Bay, three kilometres east of Watchet, Somerset, is here proposed as the type locality and section, with the base of the Hettangian Stage, at the base of the Planorbis Chronozone, being placed at the horizon currently recognized as that at which ammonites of the genusPsilocerasappear. In this section the base of the Planorbis Chronozone corresponds with the base of thePsiloceras planorbisBiozone. The proposal of this section is conditioned by the availability of comprehensive litho- and biostratigraphic information, and the ability of the section to fulfil International Commission on Stratigraphy (ICS) requirements for a candidate GSSP.
Diagenetic controls on multiphase pyritization of graptolites
Authors: Underwood Charlie J. , Bottrell Simon H. 
Published: May 2009

AbstractObservations on pyritized graptolites have revealed a variety of pyrite morphotypes, several of which often coexist within the same fossil steinkern. The commonest forms of pyrite are those consisting of size-sorted microcrysts, which show degrees of ordering ranging from well-ordered framboids to a more homogeneous, unordered groundmass. Larger, euhedral pyrite crystals may be scattered throughout the microcrystalline groundmass, or be the dominant pyrite form in themselves. ‘Floriform’ pyrite frequently overgrows earlier framboids and may act to mould the inner periderm microstructure of the graptolite. Overpyrite occurs either as a primary ‘overspill’ of internal pyrite, or as a separate, later phase.All of the diagenetic pyrite has light sulphur isotope compositions, indicating formation during early diagenesis; isotopic evidence of the relative timing of pyrite generations matches the morphological paragenesis. Under most conditions, available iron appears not to be a limiting factor in pyrite formation, with reactive organic matter only being limiting at the lowest concentrations encountered in these sediments. The availability of organic matter does, however, exert a control on the timing of fossil pyritization. At one locality, a change in diagenetic conditions has allowed for the formation of a morphologically late generation of pyrite with isotopically light and therefore apparently early diagenetic signatures.
Conodont thermal alteration patterns in Palaeozoic rocks from Belgium, northern France and western Germany
Authors: Helsen S. , Kønigshof P. 
Published: May 2009

AbstractIn this paper thermal patterns based on conodont Colour Alteration Indices (CAI) have been studied in the Devonian and Carboniferous rocks from Belgium, northern France and western Germany. Four maps (with the exception of the southeastern Rheinisches Schiefergebirge) have been compiled for the investigated area: one for the Eifelian and Givetian, a second for the Frasnian, another for the Famennian and one for the Tournaisian and Viséan. Conodonts have not been found in Cambrian rocks from Belgium and northern France and as they are scarce in the Ordovician to Lower Devonian formations of this area, it was impossible to integrate these CAI data into an isograd map. In Germany (in the eastern Rheinisches Schiefergebirge) only a few CAI values for the Lower Devonian strata are available. In contrast to the Ardennes where in general conodonts show CAI values of 3.0–5.0, indices in areas adjacent to the Anglo-Brabant Massif, e.g. in the western Namur Synclinorium and in the Eifel Hills, range between 1.5 and 2.0. Slightly higher values occur in the Campine Basin north of the Anglo-Brabant Massif. By comparison with CAI data from Belgium, conodont colour alteration indices from the same stratigraphic horizons in some areas of the northern and eastern Rheinisches Schiefergebirge are up to one index higher. In most areas of the Rheinisches Schiefergebirge the level of metamorphism corresponds to the anchizone. Regional variations in CAI data appear to be related to buried intrusions and associated hydrothermal activity. In the southeastern Rheinisches Schiefergebirge CAI data are not completely consistent but it is possible to discern an increase in coalification from the north to the south. High index values in the southern Rheinisches Schiefergebirge are believed to result from regional metamorphism and heating related to numerous intrusive bodies.
The Portsoy–Duchray Hill Lineament: a review of the evidence
Authors: Goodman S. 
Published: May 2009

AbstractThe Portsoy–Duchray Hill Lineament has been widely quoted in the literature as a major zone of discontinuities, running from Portsoy on the Banff coast to the Duchray Hill area in Perthshire. A review of the evidence indicates that there is no single structural entity running from Portsoy to Duchray Hill; the term ‘Portsoy-Duchray Hill lineament’ should be avoided. There are, however, significant along- and across-strike variations in geological history across a zone which extends from Portsoy to the Cabrach (the ‘Portsoy Line’). Certain elements can be identified also in areas further south, e.g. the Coyles of Muick shear zone and Glen Doll fault.The Portsoy Line was initiated as a zone of syn-depositional faulting, with resulting facies variations similar to those seen across the Glen Doll fault. The Portsoy Line was reactivated as a ductile shear zone during Caledonian orogenesis, while the Glen Doll fault is a later, more brittle, structure. The shear zone from Portsoy to the Cabrach forms the western branch of a system of shears which acted to focus syn-orogenic basic magmatism, and differential movement during post- metamorphic uplift. The Coyles of Muick shear zone is the most southerly example of the system of shears, and there is probably a transfer zone along Deeside between it and the Portsoy-Cabrach shear zone, now obscured in part by the Ballater Granite. The focused shear zones serve to delineate the Buchan area, with its low pressure metamorphism and distinctive structural style, from areas to the south and west where the structural level was deeper, and deformation more pervasive.
Fluid supersaturation and crystallization in porous media
Authors: Putnis Andrew , Prieto Manuel , Fernandez-Diaz Lurdes 
Published: May 2009

AbstractThe relationship between the supersaturation at the point of crystallization and the rate at which supersaturation increases has been studied from nucleation experiments on barite BaSO4, strontianite SrCO3, witherite BaCO3 and gypsum CaSO4.2H2O. The crystallization experiments have been carried out by the counter-diifusion of cations and anions through a column of porous silica gel transport medium. Nucleation is suppressed in a finely-porous medium resulting in very high values of supersaturation before crystallization from the solution begins. This threshold supersaturation for nucleation depends on the solubility of the salt, the porosity of the medium and the supersaturation rate. Nucleation inhibitors were used to extend the range of supersaturation attainable. In all cases the experimental data fits the general expression: rate of change of supersaturation ∝ (threshold supersaturation)m. These results are compared to previous work from the field of chemical engineering on the relationship between supersaturation, volume and cooling rate in aqueous salt solutions. These experiments have important implications to supersaturation in natural fluids and subsequent crystallization in relation to geological problems including crystallization in low temperature sedimentary environments and fluid-rock ratios in hydrothermal mineral deposits.
A revision of Ordovician series and stages from the historical type area
Authors: Fortey R. A. , Harper D. A. T. , Ingham J. K. , Owen A. W. , Rushton A. W. A. 
Published: May 2009

AbstractThis paper is a revision of the standard chronostratigraphy of the Ordovician of the historical type area in England and Wales. The revision is a response to the need for more precise definitions of series and stages, especially for practical international correlation. In some cases this has entailed moving horizons for Series bases away from those in the classical sections. The scheme will be used as the standard for a forthcoming revision of the Correlation Chart of the British Ordovician System. The Ordovician is divided into five series: Tremadoc, Arenig, Llanvirn, Caradoc and Ashgill. The Llanvirn is extended to include part of the classical Llandeilo Series, which is included within it as a stage. Where stage subdivisions of standard series have not yet been defined, as in the Tremadoc, they are proposed in this paper. However, Bancroft’s fine stadial divisions of the Caradoc, which have been criticized for their brevity and local utility, are combined into four new stages, which will have wider application. The former Caradoc subdivisions are retained as substages for the purposes of regional correlation.
Pterosaur fossils from the Cretaceous of Chile: evidence for a pterosaur colony on an inland desert plain
Authors: Bell C. M. , Padian K. 
Published: May 2009

AbstractA 2-m-thick bed of sandstone and conglomerate in early Cretaceous desert sediments in the Andes of northern Chile contains thousands of scattered pterosaur bones. The bed displays sedimentary features which suggest that it was the product of a single major flood event. It seems possible that a large pterosaur colony was overwhelmed by the waters of an exceptional flood sweeping across a flat alluvial plain.
Palaeomagnetism of Late Ordovician igneous intrusions from the northern Welsh Borderlands: implications to motion of Eastern Avalonia and regional rotations
Authors: Piper J. D. A. 
Published: May 2009

AbstractThe palaeomagnetism of a Late Ordovician dolerite suite widely distributed in the northern Welsh Borderlands has been investigated to evaluate (i) regional rotations associated with later deformations and (ii) Lower Palaeozoic latitudes of Eastern Avalonia. Only local effects of Acadian and Variscan overprinting are observed in this region and most bodies appear to preserve a primary cooling-related magnetization. Magnetic properties in the Breidden Dolerite are related to primary igneous differentiation and a dual polarity characteristic remanence (D/I = 333.1/−71.6°, 6 sites, α95 = 10.4°) predates Late Ordovician folding. Dolerites elsewhere in the Breidden Hills Inlier record the same reversal of remanence and the combined mean (D/I = 314.3/−72.8°) is rotated clockwise from the mean remanence (D/I = 291.5/−59.5°, 21 sites, α95 = 6.0°) in a similar dolerite suite within the adjoining Shelve Inlier which is also of dual polarity and predates Late Ordovician folding. The difference in magnetic declinations is similar to the rotation of Late Ordovician fold axes and fracture systems between the two inliers and is probably the resultant effect of local rotation, possibly about a constraining bend in the Severn Valley Fault System. The Moel-y-Golfa Andesite of Caradocian (Soudleyan) age has a remanence (D/I = 294.3/−50.4°, 13 samples, α95 = 2.8°) which study of an adjoining volcanic conglomerate shows to be of primary cooling-related origin. The equivalent palaeolatitude is ˜ 31° S in early Caradocian times. A similar estimate is derived from a probable diagenetic overprint in the contemporaneous Castle Hill Conglomerate at Montgomery. The Mynydd-Bryn Andesite in the Berwyn Inlier, of probable similar origin and age to Moel-y-Golfa, has a magnetization of opposite polarity but similar inclination (D/I − 239.1/47.4°, 14 samples, α86 = 5.5°). Declination differences between these volcanic outcrops are a possible signature of later block rotations between the Lower Palaeozoic inliers and identify the importance of terrane definition in analysis of Lower Palaeozoic palaeomagnetic results from the Caledonides. A dolerite sheet complex at Hendre in the Berwyn Hills has a younger remanence (D/I − 182.3/ − 3.0°, 20 samples, α95 = 7.8°), probably of mid-Carboniferous age.The collective Upper Ordovician results define a rapid movement of the Avalonian Plate, probably spanning no more than 10 Ma, from ˜ 30° S in early Caradocian times to ˜ 57° S prior to folding of the dolerites in late Caradocian to early Ashgill times. This motion into higher southerly palaeolatitudes marks a reversal of the motion of Avalonia into more shallow southerly palaeolatitudes between Arenig and Llanvirn times and shows that Ordovician closure of the Iapetus Ocean was more complex than recognized hitherto.