bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Pitts Head Tuff Formation: a subaerial to submarine welded ash-flow tuff of Ordovician age, North Wales
Authors: Reedman A. J. , Howells M. F , Orton G. , Campbell S. D. G 
Published: May 2009

AbstractThe Pitts Head Tuff Formation, of Ordovician (Caradoc) age, was emplaced as a thick (c. 700 m) intracaldera sequence and two outflow units comprising welded acidic ash-flow tuff. The Pitts Head pyroclastic flows were erupted subaerially but the lower and most extensive of the outflows crossed a shoreface, and continued for several kilometres offshore. The flow entered the sea without disruption and, following deflation and tuff emplacement, displaced the shoreface several kilometres to the east and northeast. Post-eruption subsidence in the northeast resulted here in the rapid establishment of environments deeper than had previously existed.The lower outflow tuff is parataxitically to eutaxitically welded in both the subaerial and marine environments. The extremely regular plane-parallel welding foliation of the subaerial tuffs, however, contrasts with the locally highly deformed foliation of the tuff deposited beyond the shoreface. The deformed foliation, associated with irregular zones of intense siliceous nodule development, is ascribed to the upward streaming of water vapour generated at the tuff/sediment boundary. Elsewhere rheomorphism within the tuff was caused by instability resulting from emplacement on slopes related to faulting. Continued movement initiated extensive brecciation, detachment, and local gravity sliding of large rafts of tuff.
Proterozoic geological evolution of the northern Vestfold Hills, Antarctica
Authors: Passchier C. W. , Bekendam R. F. , Hoek J. D. , Dirks P. G. H. M. , de Boorder H. 
Published: May 2009

AbstractThe presence of polyphase shear zones transected by several suites of dolerite dykes in Archaean basement of the Vestfold Hills, East Antarctica, allows a detailed reconstruction of the local structural evolution. Archaean and early Proterozoic deformation at granulite facies conditions was followed by two phases of dolerite intrusion and mylonite generation in strike-slip zones at amphibolite facies conditions. A subsequent middle Proterozoic phase of brittle normal faulting led to the development of pseudotachylite, predating intrusion of the major swarm of dolerite dykes around 1250 Ma. During the later stages and following this event, pseudotachylite veins were reactivated as ductile, mylonitic thrusts under prograde conditions, culminating in amphibolite facies metamorphism around 1000–1100 Ma. This is possibly part of a large-scale tectonic event during which the Vestfold block was overthrust from the south. In a final phase of strike-slip deformation, several pulses of pseudotachylite-generating brittle faulting alternated with ductile reactivation of pseudotachylite.
A new early Ordovician Didymograptid, and its bearing on the correlation of the Skiddaw Group of England with the Tøyen Shale of Scandinavia
Authors: Maletz J. , Rushton A. W. A. , Lindholm K. 
Published: May 2009

AbstractDidymograptus (s.l.) rigoletto sp.nov. is a distinctive species in the balticus group of didymograptids occurring in the Tøyen Shale (Lower Ordovician). In three localities in Sweden it has a short range near the top of the range of Tetragraptus phyllograptoides, and it occurs at about the same level at localities in the Oslo region, Norway; at most of these localities it occurs within the range of Tetragraptus of the approximatus group. Its presence in the Skiddaw Group of the English Lake District indicates the occurrence there of the basal Arenig (sensu lato), equivalent to the T. phyllograptoides Biozone of Scandinavia and the T. approximatus Biozone (= Lancefieldian 3) of the Australasian succession.
Palaeoenvironments and palynofacies of a pulsed transgression: the late Devonian and early Dinantian (Lower Carboniferous) rocks of southeast Wales
Authors: Davies J. R. , McNestry A. , Waters R. A. 
Published: May 2009

AbstractTwo boreholes in the Vale of Glamorgan have provided new data on the nature of the early Dinantian (Courceyan) transgression in South Wales. This transgression is manifested by the transition from the largely fluviatile, late Devonian, Upper Old Red Sandstone (Quartz Conglomerate Group) to the predominantly marine, early Dinantian, Lower Limestone Shale Group. The marine sequence comprises five shoaling upwards cycles, constructed from a suite of sedimentary lithofacies which record deposition in environments ranging from coastal plain, peritidal, lagoon, barrier and embayment to subtidal, open marine shelf. Each cycle represents a pulse of the transgression, and each successive pulse appears to have been larger than the preceding one, introducing progressively less restricted and more distal marine environments.Thirty-seven samples were processed for palynological analysis. Miospore biozonation supports the cycle correlations between the two boreholes, suggested by the sedimentary event stratigraphy. Detrital kerogens from the samples comprise both terrestrially derived and marine types in varying proportions. Each kerogen type is described as well as the size, sorting and preservation of each assemblage. A palynofacies profile is presented for eachof the depositional environments recognized.
Marine event beds and recolonization surfaces as revealed by trace fossil analysis
Authors: Frey R. W. , Ring R. Gold 
Published: May 2009

AbstractTurbidites and tempestites exhibit characteristic distributions of trace fossils. To gain maximum advantage of the sedimentological and palaeoecological significance of these traces, an attempt should be made to relate each trace to the associated colonization surface. This approach allows traces initiated at the normal top of an event bed to be distinguished from traces that subsequently passed into the bed from a higher colonization level or were initiated on the eroded surface of the bed.
An iridium anomaly in the Ludlow Bone Bed from the Upper Silurian, England
Authors: Schmitz B. 
Published: May 2009

AbstractThe Ludlow Bone Bed in the Upper Silurian of the Welsh Borderland shows an anomalously high concentration of iridium (0.49 ppb) compared with background (0.040 ppb Ir). Considering the overall major and trace element pattern and the mineralogy of the bone bed, it appears that the bulk of their has precipitated from sea water and is not primarily related to an asteroid impact event. A secondary relation of the Ir to such an event, however, cannot be excluded. The profound sedimentological similarity (skeletal sands and hummocky cross-stratification) between the Ir-carrying ‘storm deposit’ at the Cretaceous–Tertiary boundary at Brazos River, Texas, and the LBB and overlying sediments may indicate such a relation.
The record and stratigraphie implications of organic-walled microfossils from the Ediacaran (terminal Proterozoic) of South Australia
Authors: Jenkins Richard J. F. , McKirdy David M. , Foster Clinton B. , O'Leary Teresa , Pell Stephen D. 
Published: May 2009

AbstractTwo assemblages of organic-walled microfossils have been recognized in drillcore samples from the late Proterozoic Rodda Beds in theeastern Officer Basin, South Australia. The fossils include tube-like remains and large, simple and sculptured acritarchs. Lithostratigraphic studies and seismic information, in conjunction with previous (albeit limited) acritarch finds, allow local correlation of the Rodda Beds with Ediacaran or terminal Proterozoic sequences in the northern Adelaide Fold Belt (site of the nominated Ediacaran stratotype). The new palynofloras are comparable withacritarch assemblages in the Amadeus Basin of central Australia, and suggest tentative correlations with sequences in China and the U.S.S.R. The presence of isotopically heavy marine carbonate in the lower fossiliferous horizons of the Rodda Beds (σ13CPDB= +3 to +6%0) is consistent with isotopic data from the equivalent interval in China. In contrast, the upper fossiliferous strata occur higher in the Rodda Beds where carbonate is significantly lighter (σ13CPDB= -1 to + 3%0).
Active alluvial systems in the Korla Basin, Tien Shan, northwest China: sedimentation in a complex foreland basin
Authors: Allen M. B. , Windley B. F. , Chi Zhang 
Published: May 2009

AbstractThe Tien Shan is a Cenozoic orogenic belt in central Asia caused by the post-collisional convergence of India with Asia that reactivated Palaeozoic faults. The Korla Basin is a complex foreland basin within the Chinese Tien Shan; elongate sub-basins within it have received sediment from both the hangingwall and footwall blocks above and below reverse faults on their northern margins. The footwall blocks are themselves uplifted by the next fault to the south: the greater part of the sediment supply measured by area comes from the footwall block. This sediment supply pattern is analogous to that of extensional half-graben.
Rb-Sr age determinations of rocks from the Okenyenya igneous complex, northwestern Namibia
Authors: Milner Simon C. , Le Roex Anton P. , Watkins Ronald T. 
Published: May 2009

AbstractThe Okenyenya igneous complex is one of a suite of intrusions which define a prominent northeast-trending linear feature in Damaraland, northwestern Namibia. Precise Rb–Sr internal isochron ages range from 128.6 ± 1 to 123.4 ± 1.4 Ma for the major phases of intrusion identified within the complex. The tholeiitic gabbros forming the outer rings of the complex, and the later alkali gabbros which form the central hills, cannot be distinguished in terms of Rb–Sr ages, although field relations clearly indicate the younger age of the latter. The intrusionsof nepheline-syenite and essexite comprising the mountain of Okenyenya Bergon the northern edge of the complex give ages of 123.4 ± 1.4 and 126.3 ± 1 Ma, respectively, and form the final major phase of intrusion. The ages obtained for early and late intrusive phases define a minimum magmatic ‘life-span’ of approximately 5 Ma for the complex. The determined age of the Okenyenya igneous complex (129–123 Ma), when taken together with the few reliable published ages for other Damaraland complexes (130–134 Ma), suggests that these sub-volcanic complexes were emplaced contemporaneously with the widespread Etendeka volcanics (˜ 130 Ma), and relate to magmatism associated with the breakup of southern Africa and South America with the opening of the South Atlantic Ocean. The linear distributionof intrusions in Damaraland is interpreted to be due to magmatism resultingfrom the upwelling Tristan plume being focused along a structural discontinuity between the Pan-African, Damaran terrain to the south, and Proterozoiccratonic basement to the north.
The distribution, geometry and kinematic significance of Caledonian buckle folds in the western Moine Nappe, northwestern Scotland
Authors: Alsop G. I. , Holdsworth R. E. 
Published: May 2009

AbstractWithin internal regions of orogenic belts, systems of ductile thrusts and folds may form which are geometrically and kinematically analogous to those observed in foreland thrust belts. The Moine Nappe of Sutherland, northwestern Scotland, developed during WNW-directed Caledonian displacements under amphibolite facies conditions. Broad zones of mylonite associated with the ductile Ben Hope and Moine thrusts both contain numerous, small-scale folds which can be attributed to transient flow perturbations. It is possible to isolate and differentiate generations of such folds basedon their association with particular major thrust zones and'or their geometry. In regions of lower strain between these thrusts, there are a series ofkilometre-scale buckle folds, the axial traces of which define arcuate trends. Those with hinges orthogonal to transport are northwestvergent, whilst those plunging subparallel to the mineral lineation display variable vergence. The spatial distribution of these geometries suggests a causal relationship with displacements on specific underlying thrusts. We propose that they reflect larger (kilometre-scale), and possibly longer-lived flow perturbations. The transport parallel folds are persistent features that often centre on earlier structural culminations, and are thought to reflect components of differential shear. The most prominent set of regional buckle folds root downwards into the ductile Moine Thrust, and openly refold the structurally overlying Ben Hope Thrust and its associated buckle folds, thus supporting a foreland propagating sequence of ductile displacements.
Structural evidence supporting a remnant origin of patchy charnockites in the Chilka Lake area, India
Authors: Bhattacharya S. , Sen S. K. , Acharyya A. 
Published: May 2009

AbstractDark patches of charnockitic rocks characterized by orthopyroxene occur within garnetiferous granite gneisses (leptynites) in a granulite-migmatite suite around the Chilka Lake, Orissa, within the Eastern Ghats belt in the Indian Precambrian. Analysis of structures of different scales observed in this terrain establishes the presence of three phases of deformation. S1is pervasive in the metapelitic granulites (mainlykhondalite), while in the migmatite complex composed of leptynites, charnockites and quartzofeldspathic veins, S1is present exclusively within the charnockite lenses and bands, and shows different stages of obliteration in the associated leptynites. Thus, the charnockite patches must be earlier than the surrounding migmatitic rocks. The charnockite patches and the surrounding leptynitic gneisses are chemically quite different and the two rock types are not related by any prograde or retrograde transformation. The shapes and disposition of charnockite patches in the mixed exposures are found to be largely controlled by the third phase of folding and locally associated shearing. The kinematics of this late deformation are not favourable for fluid ingress from deeper levels.
Evidence on the deep structure of the Anglo-Brabant Massif from gravity and magnetic data
Authors: Lee M. K. , Pharaoh T. C. , Williamson J. P. , Green C. A. , De Vos W. 
Published: May 2009

AbstractGravity and aeromagnetic data from Britain, Belgium and the southern North Sea have been compiled to provide coverage of the greater part of the Anglo-Brabant Massif. Colour pseudo-relief maps of the gravity and magnetic fields highlight important anomalies and trends which provide new information on the structure of the massif and its margins. Within the massif, prominent SSE-trending geophysical lineaments define the margins of distinctive blocks within the upper crust. These are cross-cut on the northeastern margin of the massif by prominent ESE- and SE-trending magnetic and gravity lineaments. The possible history and origin of the more prominent geophysical anomalies and lineaments are considered. Integrated modelling of the potential field data has been carried out along the BIRPS MOBIL-7 seismic reflection line to provide an interpretation of crustal structure across the northeast margin of the massif constrained by all three datasets. The principal features of the model are a non-reflective, non-magnetic upper crust, interpreted as the Caledonian fold–thrust belt, overlying a heterogeneous middle–lower crust with laterally varying reflectivity, magnetization and density. ESE-trending magnetic anomalies along the northeast edge of the massif are explained in terms of an irregular mid-crustal magnetic layer with a susceptibility comparable to that of the Tubize Group in the Brabant Massif. The top of this body is coincident with prominent dipping mid-crustal reflectors observed on the seismic reflection profile and its overall geometry is compatible with mid-crustal imbrication inferred from the seismic data.
New evidence that the Lower Cambrian Leny Limestone at Callander, Perthshire, belongs to the Dalradian Supergroup, and a reassessment of the ‘exotic’ status of the Highland Border Complex
Authors: Tanner P. W. G. 
Published: May 2009

AbstractThe Lower Cambrian Leny Limestone at Callander in Scotland lies within a sequence of palecoloured grits and dark slates (here named the Keltie Water Grit Formation (KWGF)) which has lithological similarities with members of the Highland Border Complex (HBC) (Ordovician) seen elsewhere along the Highland Border. The Keltie Water Grit Formation has a transitional boundary with a grit-slate sequence of undoubted Dalradian parentage; as the ‘Leny Grits’ of previous workers include both the KWGF and part of the Dalradian sequence, this term is now rendered invalid. The entire sequence youngs upwards from the Dalradian to the top of the overlying Keltie Water Grit Formation, shares the same structural sequence and geometry, and has the same facing and vergence direction on the main cleavage. All field and petrographic data are consistent with a minimum age of post-early Cambrian for the Grampian event, the main orogenic event to affect the Dalradian. Examination of critical sections elsewhere across the Highland Border shows that there is an apparently consistent stratigraphical and structural relationship between the Highland Border Complex and the Dalradian which, as suggested by some previous workers, would require the Grampian event to be post-Arenig in age. However, we are faced with a so-far unresolved paradox that there are certain palaeontological and radiometric data which are in conflict with this conclusion, and support the alternative hypothesis that the Highland Border Complex docked with the Dalradian in post-Ordovician times.
Pyroxenous greywackes in the Southern Uplands of Scotland and their petrotectonic implications
Authors: Styles M. T. , Perez-Alvarez M. , Floyd J. D. 
Published: May 2009

AbstractDetrital clinopyroxenes occur abundantly in several greywacke formations in the Southern Uplands, both as single grains and within andesite lithoclasts. Compositionally, these pyroxenes fall into two main groups. Those from the oldest unit, the early Caradoc Galdenoch Formation, were derived from a simple tholeiitic volcanic arc. In contrast, the pyroxenes in the younger Portpatrick (late Caradoc) and Glenlee (Ashgill) Formations and the Gala Group (early Llandovery), show initial strongly calc-alkaline affinities, followed by a more complex calc-alkaline to transitional (calc-alkaline to tholeiitic) volcanic arc signature. The latter may be due to a mixture of calc-alkaline and tholeiitic components. A presently exposed source for the andesites has not yet been established, although the Ballantrae Complex is a potential candidate for a tholeiitic component.
Nd-isotope study of provenance patterns across the British sector of the Iapetus Suture
Authors: Stone P. , Evans J. A. 
Published: May 2009

AbstractThe Southern Uplands greywacke succession (Scotland) accumulated at the Laurentian margin of the Iapetus Ocean. It was sequentially incorporated into an imbricate, accretionary thrust complex until closure of the ocean. Thereafter the thrust belt propagated across the suture zone as a foreland thrust belt directed towards the hinterland of Avalonia. A foreland basin migrating ahead of the thrust belt was the depositional site for the southernmost Southern Uplands units and the Windermere Supergroup (English Lake District). A Nd-isotope study has shown that juvenile ophiolitic detritus was introduced into the oldest, mid-Ordovician, Southern Uplands greywackes before two distinct provenance areas evolved: one supplying juvenile andesitic detritus in addition to a quartzo-feldspathic component, the other Proterozoic and exclusively quartzo-feldspathic. Bimodal composition continued into the early Silurian but was overlapped from late in the Ordovician by greywackes with intermediate Nd-isotope composition. This was not a simple mixing effect since the andesitic component is not represented and the necessary juvenile component comes from granodioritic and felsitic lithologies. Intermediate eNd values are then a consistent feature through the Silurian both in the younger strata of the Southern Uplands and in the earliest foreland basin turbidites of the Windermere Supergroup. The transition suggests cessation of volcanicity and erosion of deeper levels of the provenance terrane(s), possibly linked to the evolution of the basin system from active margin, accretion-related, to a foreland setting. To the north of the Southern Uplands terrane, beyond the Southern Upland Fault, a Caradoc to Wenlock turbidite sequence occupies inliers within the Midland Valley. The older greywackes contain abundant juvenile ophiolite and plutonic detritus in addition to a quartzofeldspathic metamorphic component; there are similarities with the most northerly part of the Southern Uplands. From the late Ordovician, εNd values systematically decline so that early Llandovery Midland Valley greywackes are exclusively quartzo-feldspathic, derived from an ancient source indistinguishable in isotopic terms from that periodically supplying the Southern Uplands. In general the Llandovery Midland Valley provenance was significantly more mature than that contemporaneously supplying the Southern Uplands. Thereafter, the Midland Valley latest Llandovery and early Wenlock greywackes contain a higher proportion of a juvenile component, and by the early Wenlock, greywackes from the Midland Valley, Southern Uplands and Lake District terranes are similar in terms of εNd. A common provenance seems likely and suggests that by the mid-Silurian all three terrenes were in close proximity.
Late Caradoc graptolitic faunal gradients across the Iapetus Ocean
Authors: Zalasiewicz J. A. , Rushton A. W. A. , Owen A. W. 
Published: May 2009

AbstractLate Caradoc graptolite assemblages across the Iapetus Ocean in Wales and Scotland became progressively more disparate despite the narrowing of the ocean. We compare faunal distributions in continuous sections from opposite sides of Iapetus, at Whitland in South Wales and Hartfell Score in the Southern Uplands of Scotland. A comprehensive graptolite range-chart is given for each. The graptolite assemblages from the clingani Biozone are subdivided into a lower Ensigraptus caudatus Subzone and upper Dicellograptus morrisi Subzone at both localities, though the faunas differ in detail. Higher in the sequence, the distinctive Scottish linearis Biozone fauna is not recognizable at Whitland, its presumed equivalent being a fauna dominated by variable morphotypes of the genus Normalograptus. This suggests that environmental gradients (depth and/or temperature) were changing more rapidly than the geography. Significantly, the subsequent inception of limestone deposition at Whitland was approximately contemporaneous with widespread replacement of black mudstones by oxic, bioturbated sediments elsewhere in the Welsh Basin and in Scotland. This was possibly a response to an early phase of cooling prior to the end-Ordovician glaciation. In Wales the claimed hiatus at the Caradoc-Ashgill boundary may rather reflect biofacies variation.
The first record ofCooksoniafrom South Americain Silurian rocks of Bolivia
Authors: Morel E. , Edwards D. , Rodriguez M. Iñigez 
Published: May 2009

AbstractPlant megafossils resemblingCooksonia caledonicaLang aredescribed from the Kirusillas Formation in southern Bolivia.Faunal and lithological evidence together with field relation-ships advocate a late Silurian (Ludlow) age. Palaeocontinentalreconstructions suggest that the plants grew on the western edgeof Gondwana at 50–60° S and indicate thatCooksoniahadspread to higher latitudes soon after its appearance in the Wenlock.