bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cryptic exposure horizons in the Carboniferous Limestone of Portishead, Avon
Authors: Faulkner T. J. , Wright V. P. , Peeters C. , Garvie L. 
Published: February 2007

AbstractTwo unusual subaerial exposure horizons containing fibrous columnar calcite crystals are described from the (early Chadian) Lower Carboniferous of Portishead, near Bristol in southwest Britain. The lower horizon overlies the Courceyan Black Rock Limestone (mid‐ramp facies) and is separated from the upper horizon by the Sub‐Oolite Bed and is overlain by the Chadian Gully Oolite (both are inner ramp deposits).Regionally the Portishead Palaeosol Beds are interpreted as forming part of extensive emergent surfaces which developed along the southern margin of the Welsh–Brabant Massif. They correlate with similar subaerial exposure horizons in Belgium and southern Germany, and may be the product of a proposed major eustatic sea level fall at the end of the Courceyan.
Tide versus storm in Epeiric coastal deposition: Two Proterozoic sequences, India
Authors: Bose Pradip K. , Chaudhuri Amit K. 
Published: February 2007

AbstractThe relative importance of tides and storms in coastal sedimentation in ancient epeiric seas is frequently problematical. Here we appraise the depositional regimes in two Proterozoic Vindhyan formations in India with the aim of elucidating the records of each of these processes. The respective products of the two processes are not easily distinguished as both of them entail repeated fluctuations in water level and depositional energy. Two orders of fluctuation are recognized in both formations. The nature and scale of these two orders of fluctuation along with high‐resolution facies analysis make the distinction between the respective products of the two processes possible. Many of the features so long counted as characteristics of tidal rhythms, in the studied formations, exclusively or frequently manifest waxing and waning of storms or fairweather–storm cyclicity. This study highlights the need for reevaluation of ancient coastal sequences in epeiric setting.
Stratigraphy and sedimentology of lower carboniferous (Dinantian) boreholes from West Co. Meath, Ireland
Authors: Strogen Peter , Jones Gareth Li. , Somerville Ian D. 
Published: February 2007

AbstractThe 2‐km deep Athboy Borehole (1439/2) together with the lower part of boreholes EP30 and N915 form a standard type section for strata of Dinantian (Courceyan to Asbian) age in west Co. Meath. Above a thin basal red‐bed siliciclastic sequence, the marine Courceyan shelf succession is almost 600 m thick. It comprises the Liscartan, Meath, and Moathill Formations of the Navan Group and the Slane Castle Formation of the succeeding Boyne Group. The shallow‐water limestones include micrites, oolites, and sandy bioclastic packstones and grainstones with subordinate skeletal wackestones and shales. Lateral facies changes from north to south in the Navan area suggest deepening across a shelf towards a depocentre further to the south around Trim.The deeper‐water Waulsortian Limestones of late Courceyan to Chadian age (Feltrim Formation, ca. 213 m thick) form a series of five sheet‐like mudbanks, interbedded with generally thin units of nodular crinoidal limestones and shales. The mudbanks are formed of bryozoan‐rich peloidal wackestones and lime‐mudstones with phase C and D components. Rare soft‐sediment breccias occur at the bottom and top of banks.The succeeding Fingal Group commences with a thin interval (3–20 m) of black shales, laminated packstones, and micritic limestones of Chadian age, the Tober Colleen Formation. This is followed by the Lucan Formation (Chadian to Asbian) predominantly of laminated and graded calciturbidites, laminated sandstones, cherts, and black shales, which is over 1300 m thick. Ten sedimentary units have been informally defined, based on lithofacies and facies associations. The oldest unit, the Tara Member, is characterized by proximal debris‐flow breccia deposits and nodular mudstones. A thick bioturbated micrite and shale unit (Ardmulchan Member) in the middle of the formation is overlain directly by a coarse oolitic and crinoidal grainstone unit (Beauparc Member). Near the top of the formation is a distinctive unit of coarse‐grained laminated sandstones and shales (Athboy Member). The highest rocks in the Borehole are clean thickly‐bedded limestones of the Asbian Naul Formation (>90 m thick). The youngest Dinantian strata in the area, the Brigantian Loughshinny Formation, marks a return to shale‐dominant basin sedimentation.The significance of this work lies in the fact that the Athboy borehole is the longest continuously cored borehole in the Carboniferous of Ireland and provides a continuous sedimentary and biostratigraphic record for the northern part of the Dublin Basin. Foraminiferal biozones (Cf2–Cf6) have been recognized in this and in borehole N915, and Stage boundaries identified, which can be applied throughout the Basin. The sedimentary record for the Lucan Formation indicates four tectonic pulses during the Viséan, in the late Chadian/early Arundian, mid‐Arundian, Holkerian, and late Holkerian/early Asbian.
Granitoids: Main petrogenetic classifications in relation to origin and tectonic setting
Authors: Barbarin Bernard 
Published: February 2007

AbstractComparison of the twenty most frequently used petrogenetic classifications of granitoids is summarized using petrography, nature and abundance of enclaves, mineralogy, major and trace element, and isotope geochemistry. This comparison indicates considerable agreement between most authors concerning the main divisions. Differences result either from different genetic models or from the weighting of the criteria used, such as nature of the source, relative proportions of crustal and mantle contributions, magmatic processes, and types of emplacement. In the classification proposed here, three main groups of granitoids correspond respectively to a crustal, a mantle, or a mixed (crustal and mantle) origin of the magmas. Each of these main groups is subdivided into two or three types. Distinct petrographic, mineralogical, and chemical characteristics result from differences in the origin and tectonic setting of the granitoid magmas. Consequently, granitoids with well‐defined petrographic, mineralogical, chemical features and ages may provide information on the changes of tectonic settings with space, time, or both, i.e. they may be used as geotectonic tracers.
The Flamanville Granite (Northwest France): An unequivocal example of a syntectonically expanding pluton
Authors: Brun J. P. , Gapais D. , Cogne J. P. , Ledru P. , Vigneresse J. L. 
Published: February 2007

AbstractThe Flamanville pluton was emplaced during the upper Carboniferous in Palaeozoic sedimentary cover forming one limb of the Siouville syncline, a Hercynian kilometre‐scale fold in Normandy, Northwest France. We review the geological environment of the pluton with special emphasis on the Siouville syncline. The features described include gravity data, metamorphic environment, fold patterns in the contact metamorphic aureole, trajectories of principal strains in and around the pluton, finite strain and anisotropy of magnetic susceptibility within the pluton, and physical and kinematic aspects of pluton fabrics. The results emphasize that (1) the Flamanville pluton is syntectonic, (2) its emplacement involves lateral expansion of magma rather than spherical ballooning, and (3) granite fabrics do not reflect magmatic flow but are strain‐controlled irrespective of grain‐scale deformation processes and rheological state.The example of the Flamanville granite further suggests (1) that grain‐scale deformation features are not critical in distinguishing tectonic from magmatic origin of granite fabrics and (2) that pluton formation within the soft sediments of the shallow upper crust most likely results from lateral expansion of magma injected through the brittle crust rather than from ballooning of a diapiric body.
Syncompressional Emplacement of the Boulder and Tobacco Root Batholiths (Montana‐USA) by Pull‐apart along Old Fault Zones
Authors: Schmidt Christopher J. , Smedes Harry W. , MichaelO'Neill J. 
Published: February 2007

AbstractThe 15 major plutons comprising the 6000 km2 Late Cretaceous Boulder batholith were emplaced at mid‐ to upper‐crustal levels (<20 km) during active thrusting in the Montana thrust belt. The Tobacco Root batholith, the largest satellite pluton of the Boulder batholith (< 300 km2) was emplaced into uplifted Archean basement rocks immediately southeast of the frontal margin of the thrust belt.Emplacement of the Boulder batholith and its satellite plutons was controlled principally by three long‐lived and deeply penetrating regional fault sets. Two of these sets (a NE‐trending set and an E‐trending set) appear to have controlled the emplacement of the main mass of the batholith (Butte pluton). A third (NW‐trending) fault set controlled the emplacement of the Tobacco Root batholith and many of the smaller plutons of the Boulder batholith. The intersecting fault sets give the Butte pluton a distinctly rhomboid shape, elongate in a northeasterly direction. Geophysical data suggest that the pluton may have a flat floor at the level of the basal décollement of the thrust belt (∼17km).One mode of pluton emplacement consistent with a rhomboid pattern and with a compressional tectonic setting is the filling of the pull‐apart regions of shear zones. We propose that the main mass of the Boulder batholith was emplaced along a pull‐apart within a segment of a thin‐skinned thrust sheet during ENE translation in the thrust belt. Sinistral slip on the E‐trending faults at the north and south margins allowed the rhomboid‐shaped cavity to form within the thrust sheet above the basal décollement and to progressively fill with magma below a roof of cogenetic volcanic rocks.Late Cretaceous movement on the NW‐trending fault set was oblique with roughly equal components of sinistral slip and reverse slip. The main mass of the Tobacco Root batholith is elongate in a northwesterly direction between two of these faults and has a crudely rhomboid map pattern. We suggest that it, too, was emplaced by filling a sinistral pull‐apart between these faults.
The genesis of tin–uranium granites in the Scottish Caledonides: Implications for metallogenesis
Authors: Plant J. A. , Henney P. J. , Simpson P. R. 
Published: February 2007

AbstractThe genesis of granites enriched in Sn and U and their role in the formation of Sn–U deposits is reviewed with particular reference to studies of geochemical, geophysical, and geological data sets from the Scottish Caledonides based on image analysis studies.The chemistry and tectonic setting of radioelement‐enriched granites some of which are also enriched in Sn (e.g. Cairngorm intrusion) is distinct from that of the more commonly occurring calc‐alkaline granites. On mantle‐normalized diagrams they are enriched in U, Th, Rb, Nb, Ta, Li, F, Be, B, and Sn with marked depletion of Sr, Ba, Ti, and P; and on chondrite normalized REE diagrams they have high REE with LaN/LuNvalues of 1·8–6 and marked negative Eu anomalies (Eu/Eu* 0·3). These features are characteristic of Sn–U granites from S.W. England (Dartmoor) and elsewhere. Geophysical data indicate that the Caledonian Sn–U granites are the high points of a buried batholith (the East Grampian batholith) with a length of approximately 100km, breadth of about 40km, and depth of approximately 7–8km. The batholith is discordant to the Caledonian structural grain and was emplaced post‐orogenically, probably in tensional pull‐apart structures.Petrogenetic models and isotopic data for the Cairngorm granite preclude ‘S’‐type crustal melting models for its genesis; instead the preferred model involves combined assimilation and fractional crystallization (AFC) as the result of the addition of dioritic magma to the lower crust followed by up to 50 per cent fractional crystallization. The concentration of Sn, F, and radioelements in the granite magmas, the release of heat as the result of protracted fractionation, the large volumes of the intrusions, and their emplacement into fault systems are factors favouring the formation of Sn and U deposits. The high calculated heat production of such intrusions and their emplacement into faults along which reactivation can occur may explain the association of such granites with hydrothermal ore deposits formed long after magmatic cooling.Overall the role of granites in ore formation is complex and reflects such factors as the chemistry, heat production (contents of U, Th, and K), density, permeability, and response to deformation of intrusions as well as the availability of water in the rocks into which they are emplaced.
The Millstone Grit (namurian) of the southern pennines viewed in the light of eustatically controlled sequence stratigraphy
Authors: Read W. A. 
Published: February 2007

AbstractThe overall lithological succession in the Millstone Grit of the southern Pennines was most probably controlled by glacial‐eustatic sea‐level oscillations and may be interpreted in terms of the systems tracts of sequence stratigraphy. Bands containing thick‐shelled goniatites represent ‘condensed sections’ formed at times of maximum flooding. Turbidite‐fronted deltas, marking major basin‐filling episodes, resemble ‘lowstand systems tracts’. However all sand influxes did not necessarily occur during lowstands. Millstone Grit sheet deltas and elongate deltas resemble lobate and birdfoot deltas in Recent ‘highstand systems tracts’. The prograding fluviodeltaic complexes at the tops of some major turbidite‐fronted deltas were braid deltas. So was the sheet‐like channel complex of the Rough Rock at the top of the Millstone Grit, but this was probably part of a ‘highstand systems tract’.
The biostratigraphy and formational relationships of the upper aeronian and lower telychian (llandovery, silurian) formations of western mid‐wales
Authors: Loydell David K. 
Published: February 2007

AbstractThe stratigraphical relationships of the upper Aeronian‐lower Telychian formations in the Aberystwyth area are examined in the light of a new biostratigraphical subdivision of this interval based on graptolites, in which part of the Monograptus turriculatus Biozone is divided into six subzones and the Stimulograptus halli Biozone is resurrected.In the Aberystwyth area (B.G.S. 1:50 000 Sheet 163 (1984)) there is shown to be greater diachroneity of formational —boundaries than previously recognized. Notably, the Cwmsymlog Formation facies persisted in the northeast of the area far longer than anywhere else, due to the persistence of a bathymetric high into the lower Telychian. Also, the basal beds of the Aberystwyth Grits in the west of the area are shown to be of the same age as the uppermost beds of the Devil's Bridge Formation in the east. Thus for a short period the area was subject to turbiditic incursions from two sources.The degree of diachroneity of the base of the Aberystwyth Grits Formation as a whole is less than previously thought — the oldest beds are approximately one subzone older in the south than in the north. The core of the in the clinal pericline responsible for the crescentic outcrop pattern of the Aberystwyth Grits is demonstrated to lie in the vicinity of Llanrhystud, rather than at Aberarth as previously suggested.Four new graptolite species are described and one new genus is erected.
Geochemical correlation of Ordovician flow tuffs in North Wales
Authors: Orton Geoff 
Published: February 2007

AbstractOrdovician rhyolitic tuffs in North Wales are correlated on the basis of their whole‐rock trace element composition. Multivariate statistics verify that major ignimbrite sheets are chemically unique, with Zr, Y and Nb being the most useful elements to characterize individual deposits. Fractionation processes during transport and emplacement of the pyroclastic flows results in little lateral variation in the whole‐rock geochemistry of deposits; different diagenetic histories in subaerial and subaqueous environments did not mask recognition of primary ignimbrite units. A partially welded vitric ash flow tuff is correlated with the Pitts Head Tuff ash flow sheet, and a tuff horizon previously assumed to be reworked Pitts Head Tuff is shown to be chemically most similar to the fourth member of the Capel Curig Volcanic Formation. Validity of these correlations is upheld by biostratigraphic and sedimentological evidence. The new correlations necessitate a revision of the stratigraphy in North Wales and indicate a significant lapse of time (perhaps one million years) between emplacement of the Pitts Head Tuff and eruption of the Lower Rhyolitic Tuff of the overlying Snowdon Volcanic Group.
A Rhuddanian (Silurian, lower llandovery) pelmatozoan fauna from south‐west Wales
Authors: Donovan Stephen K. 
Published: February 2007

AbstractOnly two crinoid faunas of Rhuddanian or early Aeronian age have been described hitherto, both from North America. A Rhuddanian pelmatozoan fauna from Haverfordwest, Dyfed, south‐west Wales includes the cheirocrinid rhombiferan cystoidHomocystites? sp., plus the following crinoid species: the calceocrinid disparidsCalceocrinus turnbullisp. nov. andCalceocrinus? sp.; the dendrocrinid cladidDendrocrinus?gasworksensissp. nov.; the patelliocrinid monobathridMacrostylocrinus? sp. indet.; columnals of the rhodocrinitid(?) diplobathridFloricolumnus(col.) sp. cf.F.(col.)girvanensisDonovan and Clark; the rhodocrinitid diplobathridChaosocrinus ornatussp. nov.; and two indeterminate crinoid species. At the familial level this fauna shows strong similarities with coeval, but more diverse, crinoid assemblages from North America, suggesting that endemism did not develop until later in the Silurian.
Stratigraphy and structure of Devonian fluvial sediments, western Beara Peninsula, south‐west Ireland
Authors: James Andrea , Graham John R. 
Published: February 2007

AbstractA stratigraphic and structural summary of 5 km of Upper Devonian strata of south‐west Beara, part of the Munster Basin, south‐west Cork is presented. Five formations are recognized on the basis of lithofacies geometries and associations. The lowest Caherkeen Formation comprises rapidly alternating sheet‐like, plane‐bedded, low‐angle, cross‐bedded sandstones and laminated, rippled or desiccated mudrocks. The incoming of thin lenticular sandstone packages, commonly with high‐angle cross‐bedding, distinguishes the overlying Eagle Hill Formation. The succeeding Reen Point Formation comprises thicker bedsets of plane‐bedded, low‐angle and high‐angle cross‐bedded sandstones, separated by thick, massive mudrocks. Intraformational breccias and calcareous nodular siltrocks are distinctive features. The Tholane Formation is characterized by thick massive red‐green mudrocks and a general absence of coarser grained lithologies. This sequence was deposited in a terminal fluvial fan in a basin characterized by decreasing subsidence rates and gradient with time. The overlying Toe Head Formation represents the deposits of a fluvial coastal plain. It has siltrocks that are predominantly green, often with preserved fish and plant debris. There is a relative absence of high‐angled cross‐bedded sandstones and an abundance of flat‐laminated and inclined parallel‐laminated sandstones.The structure of the Beara Peninsula comprises a WSW plunging anticlinorium with a single cleavage formed during the Variscan orogeny. Evidence from locally transecting cleavages and from mapping indicates dextral transpression. Development of the three main fault trends was contemporaneous with the folding. The well‐known copper mineralization of the Allihies area is associated with east‐west fault trends, a pattern observed elsewhere in the western Munster Basin. Basement involvement during both basin development and deformation is likely, but is difficult to test.
Controls on the nucleation and growth of porphyroblasts: Kinetics from natural textures and numerical models
Authors: Carlson William D. , Denison Cambria , Ketcham Richard A. 
Published: February 2007

AbstractQuantitative textural analysis of garnetiferous rocks from diverse metamorphic environments has demonstrated that diffusionally influenced nucleation and thermally accelerated diffusion‐controlled growth are commonly among the dominant controls on porphyroblast crystallization. A new numerical model of diffusion‐controlled nucleation and growth that incorporates time as an explicit variable is capable of replicating the essential features of many of these natural porphyroblastic textures using geologically reasonable values for the kinetic parameters governing crystallization. This model has been used to interpret quantitative textural data from four rocks in which garnet grew during prograde regional metamorphism, by assuming constant heating rates and by accepting a previously published estimate for the activation energy for intergranular diffusion. From fits of the model to natural textures, estimates have been extiacted for three previously undetermined kinetic quanities that control the nucleation and growth of garnet porphyroblasts, namely the activation energy for nucleation and the pre‐exponential rate constants for nucleation and intergranular diffusion. The uncertainty in derived values for the pre‐exponential rate constant for intergranular diffusion is probably not much larger than a factor of two because it is proportional to the uncertainty in prograde heating rates, given a defined temperature interval over which crystallization occurs. The uncertainty in estimates of the activation energy and pre‐exponential rate constant for nucleation is larger, perhaps a factor of ten, because values for these quantities are derived from fits of the model to natural crystal size distributions; the precision of these estimates appears to be limited by the fact that the crystal size distributions are affected by factors not encompassed within the model (probably variable heating rates and inhomogeneity in the distribution of nutrients in the rock's precursor).
Mechanistic interactions between deformation and metamorphism
Authors: Rutter E. H. , Brodie K. H. 
Published: February 2007

AbstractThe deformability of rocks, i.e. the resistance to deformation and the mode of failure, may be strongly influenced by syn‐tectonic metamorphic reactions. Such mechanistic interactions can often be inferred from studies on naturally deformed tectonites or from suitably designed experiments. The localized nature of retrograde reactions sometimes means that the particular interaction can be inferred as a result of the preservation of both the deformed rock and its protolith, but in prograde situations recrystallization at the metamorphic peak tends to destroy microstructural evidence of the deformation mechanism.Syn‐metamorphic mechanistic interaction can be classified according to the effects of: (a) elevated fluid pressure produced during dehydration or decarbonation reactions; (b) transient grain size changes with a possible transition to grain size sensitive flow; (c) effects of changes in pore fluid chemistry and recrystallization on the resistance to plastic flow of silicates (e.g. quartz); (d) enhancement of chemical potential gradients driving diffusive creep; and (e) enhancement of plasticity through the effects of solid phase volume changes. The first three of these effects are expected to be the most important. A soil mechanics approach to the description of the flow of porous rocks provides a basis for understanding deformation during regional prograde reactions, but simple, steady‐state constitutive laws of the type used to describe plastic flow of monomineralic rocks are unlikely to be able to be applied to syn‐metamorphic deformation.