bluuebunny/crossref_metadata_2025_split huggingface dataset:
A trepostome bryozoan from the Lower Arenig of south Wales: implications of the oldest described bryozoan
Authors: Taylor Paul D. , Cope John C. W. 
Published: May 2009

AbstractA specimen of the trepostome bryozoan Orbipora from the Lower Arenig of south Wales is described and figured. This is currently the oldest unequivocal bryozoan recorded in the literature. Although mostly decalcified, the colony preserves clear remnants of the large styles which characteristically indent the zooecial apertures in Orbipora. The wide palaeogeographical distribution of Orbipora in the early Ordovician is consistent with the hypothesized planktotrophic larval phase. Theoretical considerations and evidence from the occurrence of Orbipora in south Wales suggest that nearshore clastic environments would be fruitful settings in which to search for further early bryozoans, although quality of preservation may be poorer than in offshore carbonates.
A model for stratigraphic and metamorphic inversions at Sulitjelma, central Scandes
Authors: Boyle A. P. 
Published: May 2009

AbstractThe relationship between disposition of metamorphic isograds and early strain history is examined for the Sulitjelma Fold Nappe of the central Scandes. Evidence for stratigraphic inversion and the widespread inversion of the garnet isograd is reviewed, and new evidence for the nature of early Scandian deformation is presented. A two-stage model is presented which explains the inversions by (i) an initial phase of horizontal compression resulting in crustal thickening by vertical stretching during closure of a marginal basin, followed by (ii) continued horizontal compression and crustal thickening by eastward-directed nappe emplacement. The emplacement of the Sulitjelma Fold Nappe during the latter phase of progressive simple-shear-dominated deformation was accompanied by the development of sheath fold geometries and the overturning of isotherms to produce the widespread inversion of the garnet isograd.
A trilobite fauna from the highest Shineton Shales in Shropshire, and the correlation of the latest Tremadoc
Authors: Fortey R. A. , Owens R. M. 
Published: May 2009

AbstractA rich fauna dominated by trilobites and calcified chordates has been collected in Shropshire from the Arenaceous Beds, the highest member of the Tremadoc Shineton Shale Formation, and hitherto regarded as poorly fossiliferous. This fauna shows that shelf conditions persisted longer in Shropshire than has been supposed. It is likely that even younger Tremadoc is cut out at the unconformity below the Caradoc in the Shineton Inlier. The correlation of the later Tremadoc is reviewed, and the nomenclature of British Tremadoc biozones is revised. The trilobites described here are a mixture of previously known and new forms. The nameShumardia (Conophrys) salopiensisCallaway is revived for British material traditionally assigned to the Scandinavian speciesShumardia pusilla(Sars), from which it is distinct. The new taxaLitagnostus meniscussp.nov.,Apatokephalus sarculumsp.nov. andSkljarella cracenssp.nov. are described. The type species ofAsaphellus, A. homfrayiandLeptoplastides, L. salteri, are redescribed, andGeragnostus callavei, Pseudokainella impar, andParapilekiasp. are recorded. New information on the ontogeny ofS. (C.) salopiensisandA. homfrayiis given.LitagnostusandSkljarellaare recorded from the British Isles for the first time.
A ‘reg’ palaeosol from the Lower Triassic of south Devon: stratigraphic and palaeoclimatic implications
Authors: Wright V. P. , Marriott S. B. , Vanstone S. D. 
Published: May 2009

AbstractA ‘reg’-type palaeosol occurs at the top of the Lower Triassic Budleigh Salterton Pebble Beds at Budleigh Salterton, south Devon. Its morphology supports the idea that such soils form by the introduction of wind blown fines below a surface stone layer by a process of wetting–drying and crack formation. The degree of profile development indicates a prolonged period of pedogenesis, corresponding to a major stratigraphic break. The palaeosol formed under arid conditions, and represents a change in climate during Scythian times from a semi-arid to arid regime.
The middle Lanna/Volkhov Stage (middle Arenig) of Sweden and its conodont fauna
Authors: Löfgren A. 
Published: May 2009

AbstractIn the established European conodont zonation theParoistodus originalisZone represents an interval in the upper middle Arenig or middle Lanna/Volkhov Stage. I have so far found it at 14 Swedish localities, represented in my collections by more than 116 000 conodont elements from 79 limestone samples. Presence/absence data together with major frequency shifts among conodont taxa allow the recognition of five successive phases within theP. originalisZone and the corresponding chron. Phase 1 occurs in the basal part of the zone, where an increase in frequency ofTriangulodus brevibasisandP. originalisdistinguishes it from immediately subjacent beds. Phase 2 corresponds to the (transgressive) lower middle part of the zone with an influx ofPeriodon, andDrepanoistodus basiovalisreplacingD. forceps. Phase 3 is equivalent to the upper middle part of the zone with generally more than 30% of the zonal denominator and withMicrozarkodina parvareplacingM. flabellum. Phase 4 is a short (regressive) event where the frequency ofParoistodusis drastically lowered, and phase 5 corresponds to the upper part whereParoistodusagain increases. The zone is particularly well represented at Lanna, Province of Närke, in south-central Sweden, where it also seems possible to connect the conodont succession with the standard trilobite zonation. Thus, at Lanna as well as at Finngrundet in the Bothnian Bay,Megistaspis (M.) simonfirst appears in the basal lower middle part of theP. originalisZone.
A late ultramafic suite in the Kap Edvard Holm layered gabbro complex, East Greenland
Authors: Tegner Christian , Richard Wilson J. 
Published: May 2009

AbstractThe Kap Edvard Holm Complex is an early Tertiary layered gabbro situated on the western side of the Kangerdlugssuaq fjord. Layered olivine gabbros in the Taco Point area are cut by several wehrlitic sill-like bodies which comprise a late ultramafic suite. An intrusive wehrlitic facies in the inner part of the bodies consists of olivine (+minor chrome-spinel) orthocumulate with clinopyroxene oikocrysts and interstitial plagioclase, kaersutite and phlogopite. A replacive facies which occurs in the marginal zones is texturally similar to the intrusive facies but contains no chromespinel and is more feldspathic, varying from a melanocratic olivine gabbro to a feldspathic wehrlite. It occurs where the sills wedge out laterally, in the lower contact zones where finger structures are widely developed, and in the upper contact zones where wehrlitic pipes feed melanocratic sheets, called parasol structures, which preferentially follow mafic layers in the host olivine gabbro. The wehrlites formed by the intrusion of hot, hydrous, ultrabasic magma into consolidated layered olivine gabbro. The replacive facies was formed by the volume for volume metasomatic replacement of olivine gabbro; dissolution of plagioclase was accompanied by crystallization of olivine. Some clinopyroxene was initially resorbed and later reprecipitated during this process. The relatively dense pore magma migrating upwards was restricted to pipes and spread out laterally when it encountered readily replaced mafic layers, while below the sills gabbro was replaced en masse and finger structures were formed. Similar late ultramafic suites occur in ophiolites, and their presence in the Kap Edvard Holm Complex supports suggestions that it acted as an ocean ridge type magma chamber during the initiation of early Tertiary sea floor spreading in the North Atlantic.
A new geological map of the Brabant Massif, Belgium
Authors: De Vos W. , Verniers J. , Herbosch A. , Vanguestaine M. 
Published: May 2009

AbstractA new geological map, mostly subcrop, of the Brabant Massif is presented, based on a revised lithostratigraphy of the outcrop area and on recently acquired palaeontological and lithological data from boreholes in the concealed area. New interpretations of magnetic and gravity data are used to extend the lithostratigraphical units into areas with few or no boreholes. A structural model of the western, northern and southern parts of the Brabant Massif is presented. The main anticlinal axis plunges towards the west-northwest, its core comprising Upper Precambrian (?) to Lower Cambrian terrigenous rocks which outcrop in the southeast. To the north of the main axis, younger rocks appear in regular succession, but to the southwest this picture is complicated by the occurrence of a second anticlinal structure and by a subparallel magmatic arc.
Subduction-related magmatism of late Ordovician age in eastern England
Authors: Pharaoh T. C. , Brewer T. S. , Webb P. C. 
Published: May 2009

AbstractDeep boreholes show that plutonic and volcanic igneous rocks comprise an important component of the Caledonian basement in eastern England. The isotopic compositions of these rocks reveal that many of them are of late Ordovician age (440–460 Ma), and their geochemical compositions suggest calc–alkaline affinities. The intermediate (diorite-tonalite) plutonic rocks are associated with a prominent northwest–southeast trending belt of aeromagnetic anomalies extending from Derby to St Ives, Hunts., which is interpreted to work the plutonic core of a calc-alkaline magmatic arc. It is inferred that this arc was generated by the subduction of oceanic lithosphere, possibly from the Tornquist Sea, in a south or southwest direction beneath the Midlands Microcraton in late Ordovician times. The age and geochemical composition of concealed Ordovician volcanic rocks in eastern England, and hypabyssal intrusions of the Midlands Minor Intrusive Suite in central England, is compatible with such a hypothesis.
Composite Ordovician lamprophyre (spessartite) intrusions around the Midlands Microcraton in central Britain
Authors: Thorpe R. S. , Gaskarth J. W. , Henney P. J. 
Published: May 2009

AbstractLamprophyre sills and dykes of Ordovician age were emplaced within Cambrian–Lower Ordovician sedimentary rocks around the northern margins of the Midlands Microcraton. The intrusions show internal mineralogical and chemical variations indicating emplacement as multiple intrusions of co-magmatic pulses. The chemical characteristics of the lamprophyre magmas indicate formation by small-degree volatile-rich partial melting of lithospheric mantle enriched and modified by Lower Palaeozoic subduction (Th/Ta 5.3–11.6, La/Ta 29–82.3), together with a contribution from within-plate mantle source (Zr/Yc. 6) and/or mineralogically heterogeneous lithosphere, followed by varying degrees of fractional crystallization during uprise.
Silurian fades beneath East Anglia
Authors: Woodcock N. H. , Pharaoh T. C. 
Published: May 2009

AbstractCore material from proven or probable Silurian sedimentary rocks beneath East Anglia has been re-examined. Four recognizable facies probably represent an environmental transition from anoxic basin slope or outer shelf through oxygenated outer shelf to storm-dominated inner shelf. This transition could have occurred laterally, from east to west across the Anglian Basin, or in time, from Llandovery (early Silurian) up to Př (late Silurian). Partial biostratigraphical constraints allow either interpretation, but the regional setting favours a marked facies transition through time as the Anglian Basin shallowed prior to the Acadian Orogeny. Reddening of the Silurian is mostly secondary beneath the sub-Triassic unconformity.
The early Palaeozoic evolution of northwest England
Authors: Cooper A. H. , Millward D. , Johnson E. W. , Soper N. J. 
Published: May 2009

AbstractThe Lake District and smaller Craven inliers of northwest England contain a Lower Palaeozoic sequence deposited on the Gondwanan side of the Iapetus Ocean, close to the junction with the Tornquist Sea. The Tremadoc to Llanvirn Skiddaw and Ingleton groups are deep water assemblages of turbidite, olistostrome and slump deposits, formed at a continental margin. They experienced uplift and erosion as a precursor to the eruption of two largely subaerial Llandeilo-Caradoc volcanic sequences: the tholeiitic Eycott Volcanic Group in the north and the calc–alkaline Borrowdale Volcanic Group in the central Lake District. The volcanic episodes are the earliest part of a major episode of magmatism, extending through to the early Devonian and responsible for a major batholith underpinning the Lake District. Subsidence in an intra-arc rift zone preserved the subaerial volcanic sequences. A marine transgression marks the base of the Windermere Group, which comprises a mixed carbonate–clastic shelf sequence of Ashgill age, passing upwards through the Silurian into a thick, prograding foreland basin sequence of Ludlow turbidites. Deformation of the Lower Palaeozoic sequences was possibly diachronous from north to south. It is attributed to the late Caledonian (Acadian) Orogeny and resulted in folding, cleavage and thrust development. Granitic intrusions, including those at Shap, Skiddaw and beneath the hydrothermal Crummock Water Aureole, are partly syntectonic and were therefore penecontemporaneous with this deformation event. Some thrust faulting post-dates the intrusive phase. Post-deformation Devonian conglomerates are also present locally.
Preliminary report on the geochemistry and mineralogy of the Nod Glas and related sediments (Ordovician) of Wales
Authors: Temple J. T. , Cave R. 
Published: May 2009

AbstractPreliminary results are reported of geochemical and mineralogical studies on the Nod Glas sediments of Caradoc age (clingani-linearis biozones) in Wales. Results are based on sampling at three localities in North Wales, together with a coeval section in South Wales. Data have been obtained for 21 elements by ICPAES, and for organic C, S and ignition loss. XRD analysis has provided semi-quantitative data on abundances of muscovite 2M1, quartz, albite and chlorite. Mean values of K2O, organic C, S, Cu, Zr and Ba are higher in the Nod Glas than in adjacent strata, while Fe203, MnO, MgO, CaO and P205 are lower. Analogy with the chemical composition of modern sediments reinforces the interpretation of the Nod Glas as being deposited under dysaerobic to anaerobic bottom conditions. There is considerable variation in composition between different Nod Glas sections. Analysis of mineral/chemical relationships shows some consistencies: for example, chlorite shows significant positive correlations with the heavier transition elements Mn to Zn, as well as with Li and Mg, presumably due to enrichment by adsorption of these elements onto subsequently recrystallized smectites. Other relationships are less consistent: organic C is correlated with muscovite (where it is probably held in interlayer sites as a relic from a smectite precursor) and sometimes also with albite. Inconsistencies between the sections in mineral/element interrelations may be due to diagenetic/metamorphic changes.
The use of kink bands to constrain fault displacements: an example from the Bala Lineament, Wales
Authors: Pratt W. T. 
Published: May 2009

AbstractThe Bala Lineament is a major NE-SW-striking fault zone that crosses the Lower Palaeozoic Welsh Basin. The southwest segment of it, the Tal-y-llyn Fault, mostly lies within a tract of Ordovician mudstones with few marker bands. Consequently, post-Caledonian (early Devonian) displacements are poorly understood. However, there is a close link between the distribution of kink bands and the fault zone. The kink bands provide information about the contemporary stress conditions and, in combination with slickensided fractures, give qualitative information about the various fault displacements. Matching of major folds across the fault suggests approximately 3–4 km of dextral strike-slip, probably of Lower Carboniferous age. A younger episode of normal faulting, perhaps related to Mesozoic extension, was accompanied by kink bands with more brittle characteristics.
The Nod Glas décollement of the Welsh Basin
Authors: Pratt W. T. 
Published: May 2009

AbstractStructural, petrographic and metamorphic evidence is presented for localized end-Caledonian (Acadian) décollement within a ‘black shale’ formation in the central Welsh Basin, close to the Caradoc–Ashgill boundary. Similar detachments are probably widespread in other parts of the, paratectonic Caledonides with upright folds and cleavage, particularly in sequences with strong viscosity contrasts.
The post-Devonian tectonic evolution of southern Spitsbergen illustrated by structural cross-sections through Bellsund and Hornsund
Authors: Mann A. , Townsend C. 
Published: May 2009

AbstractConstruction of cross-sections in Bellsund and Hornsund, southern Spitsbergen, using offshore and onshore structural data illustrate the main tectonic units of the region. From west to east these are: a wedge of late Cenozoic clastic sediments; a series of late Palaeozoic to early Mesozoic grabens controlled by basement faults along the west Spitsbergen margin; the Basement Horst, comprising late Precambrian to early Palaeozoic rocks deformed and metamorphosed during a mid-Palaeozoic orogeny; the Fold Belt, which forms a narrow NNW–SSE striking zone of eastward verging folds and thrusts attributed to Eocene inversion of a pre-Cenozoic basin; the Palaeogene Central Basin, deformed into a broad synclinorium and bound to the east by the Billefjorden Fault Zone. This basement lineament shows evidence of Palaeogene reactivation and may be linked to the Fold Belt by a detachment zone beneath the Central Basin. East of Spitsbergen, there is an offshore basin of possible Carboniferous age controlled by the Storfjorden Fault Zone which shows evidence of later inversion to form a positive flower structure.
Partial thermal resetting of 40Ar/39Ar mineral ages in western Spitsbergen, Svalbard: possible evidence for Tertiary metamorphism
Authors: Dallmeyer R. D. 
Published: May 2009

AbstractHornblende and muscovite within high-grade Caledonian metamorphic rocks exposed in Albert I Land (northwest Spitsbergen) display internally concordant 40Ar/39Ar age spectra providing no record of any post-Silurian thermal history. Both minerals record 420−425 Ma plateau ages indicating that relatively rapid cooling followed Silurian metamorphism. Muscovite within some metamorphic sequences exposed within the Tertiary tectonic zone of Oscar II Land (west-central Spitsbergen) displays a low-temperature 40Ar/39Ar age spectra discordance suggestive of a slight, post-Caledonian thermal disturbance. This is consistent with a post-Palaeozoic thermal overprint documented elsewhere in Oscar II Land and indicates that, at least locally, metamorphism may have accompanied the Tertiary orogeny.
Mesozoic extension versus Tertiary compression along the Billefjorden Fault Zone south of Isfjorden, central Spitsbergen
Authors: Haremo Pål , Andresen Arild , Dypvik Henning 
Published: May 2009

AbstractThe Billefjorden Fault Zone displays a complex tectonic history going back into Precambrian times. Observed thickness variations within Mesozoic sequences across the fault zone have previously been related to Mesozoic extensional movements along the fault zone. Recent structural, stratigraphical and sedimentological investigations suggest that the thicknessvariation observed across the fault zone is due to Tertiary compressional tectonics, and that Mesozoic extensional movements are minor or nonexistent.Tertiary deformation is characterized by a combined thin-skinned/thick-skinned structural style. Thin-skinned thrusting is due to the development of décollement zones in the Jurassic/Cretaceous Janusfjellet Subgroup and in the Triassic Sassendalen Group. Thick-skinned faulting is related to reverse faulting along a steep, east-dipping fault rooted in the pre-Mesozoic basement. Interacting thin-skinned thrusting and thick-skinned faulting has resulted in out-of-sequence thrusting, and is responsible for the thinning of Mesozoic sequences across the fault zone.
The Lower—Middle Cambrian stages and stratotypes from the Iberian Peninsula: a revision
Authors: Liñán E. , Perejón A. , Sdzuy K. 
Published: May 2009

AbstractLower-Middle Cambrian regional stages of the Iberian Peninsula (Cordubian, Ovetian, Marianian, Bilbilian, Acadoparadoxides and Solenopleuropsidae stages) are now reconsidered in the light of new stratigraphic and palaeontological (trace fossils, trilobites and archaeocyaths) studies. These stages are re-described with selected stratotypes and chronostratigraphic boundaries. The names Leonian and Caesaraugustian are formally proposed to replace the provisional stages of Acadoparadoxides and Solenopleuropsidae, respectively. A correlation chart of the Lower-Middle Cambrian lithostratigraphic units from the Iberian Peninsula is also presented. Two regessive-transgressive cycles are proposed to explain the lithological and palaeontological peculiarities through the Lower-Middle Cambrian sequence in the Iberian Peninsula.
Distribution and tectonic setting of Ordovician K-bentonites in the United Kingdom
Authors: Huff W. D. , Merriman R. J. , Morgan D. J. , Roberts B. 
Published: May 2009

AbstractTwenty-five Ordovician K-bentonite samples ranging in age from Llanvirn to Ashgill and representing both sides of the lapetus suture were analysed by INAA and XRF and compared on magmatic and tectonic discrimination diagrams. The proportional distribution of Nb, Y, Ti, Zr, Hf, Ta, Th and REE indicates that source volcanics were erupted in a setting that changed from subduction-related in the Llanvirn/Llandeilo to marginal basin extensional volcanism in the Caradoc/Ashgill. Welsh K-bentonites appear to be derived from volcanoes within the Welsh Basin, but K-bentonites from the Southern Uplands to not have characteristics consistent with a fore-arc setting, further suggesting a source related to ensialic marginal basin extensional volcanism.
The internal tectonic fabric of minor intrusions and their potential as regional palaeostress indicators
Authors: Borradaile Graham J. 
Published: May 2009

AbstractA suite of late-tectonic minor intrusive rocks in the Inner Hebrides of Scotland show a well developed internal tectonic fabric. This fabric has a similar orientation in adjacent intrusions and it is usually not seen in the wall rock. It is suggested that the intrusions' tectonic fabric records the effects of palaeostress over the cooling period of the intrusions and thus provides palaeostress trajectories over a geologically short period of time over the area occupied by the swarm of intrusions.
Field evidence for turbulence during flow of basalt magma through conduits from southwest Mull
Authors: Kille I. C. , Thompson R. N. , Morrison M. A. , Thompson R. F. 
Published: May 2009

AbstractThe swarm of Palaeocene inclined sheets around Loch Scridain in southwest Mull includes basaltic sheets which contain abundant metasedimentary xenoliths that show evidence for having been partially molten. In contrast with the majority of dyke-like conduits worldwide, which have essentially planar margins, the contact of one of these xenolithic sheets with Moine metasediments is irregular along a segment where it crosses interbedded psammites and pelites. Relatively fusible mica schists have been excavated by the magma, on either side of a massive refractory quartzite horizon. Furthermore, the dolerite of the sheet shows only a slight reduction of grain size, through a zone 0.5 m wide, adjacent to its margin, in contrast with the pronounced marginal chilling which characterizes most intrusions of the Loch Scridain swarm. These field relationships are interpreted as evidence that the basic magma which formed this sheet flowed with local turbulence during its emplacement. The estimated liquidus of the magma (1130 °C at 1 atm) is approximately 200 °C above the solidus of pelitic horizons in the country rock, but far below the solidus of the quartzites.