bluuebunny/crossref_metadata_2025 huggingface dataset:
The genesis of uranium in manganese and phosphorite assemblages, Timna Basin, Israel
Authors: Bar-Matthews Miryam
Published: May 2009

Uranium enrichments (up to 4000 ppm) occur in the manganese and phosphorite assemblages of the Lower Cambrian clastic marine sedimentary sequence, Timna Basin, Israel. Two types of mineralization assemblages can be defined. Sedimentary stratabound assemblages consist of uranium-enriched stratiform manganese and phosphatic laminae, diagenetic (type A) manganese nodules composed of pyrolusite and hollandite laminae and phosphorite lenses. Fission-track maps show that the uranium is homogeneously distributed within host manganese and phosphatic minerals of these assemblages. Epigenetic assemblages are mainly composed of manganese- and phosphorite-bearing veins and secondary (type B) manganese nodules with a coronadite dominant mineralogy. Uranium is depleted in these assemblages, relative to the sedimentary stratabound assemblages.

The distribution of manganese and phosphorite assemblages has a marked bimodal character. Alternation between manganese and phosphatic laminae in the stratiform deposits reflects cycles of oxidizing and reducing conditions brought about by mixing and stratification of the waters in the Timna semi-closed depositional basins. Compaction of wet sediments led to remobilization and the formation of uranium-enriched manganese nodules at the aerated sediment–water interface, and uranium-enriched phosphorite lenses below the interface in reducing conditions. Epigenesis occurred through the passage of solution fronts which recrystallized the manganese and phosphatic minerals and remobilized metallic elements, particularly uranium which was leached away and is still being remobilized today.

The mechanism of uranium uptake in manganese phases is shown most probably to involve adsorbtion of [(UO2)3. (OH)5]+ complexes on precipitating minerals. Uranium is enriched in both the pyrolusite and hollandite laminae of type A nodules, but is particularly concentrated in the former (4000–10000 ppm). Thermodynamic calculations of the relative stabilities of pyrolusite and hollandite suggest that the pH conditions of hollandite formation were close enough to the pH limit of efficient uranium adsorption to inhibit its uptake relative to pyrolusite.
Mass extinction pattern: result of chance
Authors: Noma Elliot , Glass Arnold L.
Published: May 2009

Arguments on the periodicity of mass extinction have been marred by incorrect statistical arguments. Mass extinction patterns can be best interpreted as chance fluctuations over time.
Microfossils and Precambrian–Cambrian boundary stratigraphy at Maldeota, Lesser Himalaya
Authors: Brasier M. D. , Singh P.
Published: May 2009

An assemblage of problematical microfossils of Precambrian–Cambrian boundary age is redescribed from the Chert–Phosphorite Member, at the base of the Lower Tal Formation of Maldeota in the Lesser Himalaya of India. This assemblage has previously been ascribed to various ages, from Precambrian to Cretaceous, but is held by us to contain:Maldeotaia bandalica, Protohertzina anabaricagroup, trumpet-shaped elements, acicular elements A & B, ?Conothecasp.,Ovalithecacf.multicostata, allathecid sp. A,Barbitositheca ansata, Hexangulaconulariacf.formosa, Coleoloidesaff.typicalis, Hyolithellusaff.insolitus, H.cf.isiticus, H. vladimirovae, Spirellus shankariandOlivooides multisulcatus. These compare closely with assemblages found above the base of the first,Anabarites trisulcatus–Protohertzina anabaricaZone in China and in the second,Pseudorthotheca costataZone of southern Kazakhstan. The stratigraphic setting of the Krol–Tal succession is reviewed and several similarities are noted between the Precambrian–Cambrian boundary successions of Lesser Himalaya in India and of Yunnan and Sichuan in Southwest China, indicating that correlation between them is possible at several levels.
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

The 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

The 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

Didymograptus (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

Two 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

Turbidites 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

The 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

Two 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

The 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

The 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

Within 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

Dark 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

Gravity 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

The 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

Detrital 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

The 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

Late 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

Plant 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.
The Habberley Formation: youngest Tremadoc in the Welsh Borderlands
Authors: Fortey R. A. , Owens R. M.
Published: May 2009

The Habberley Formation overlies the Shineton Shale Formation in the Shelve Inlier, Shropshire, and includes the youngest Tremadoc strata known from the Welsh Basin. It probably represents deposition during the interval cut out by the sub-Arenig unconformity in North Wales, and removed by the sub-Caradoc unconformity in the Wrekin district. There is no angular unconformity between Tremadoc and Arenig in the Shelve Inlier. The Habberley Formation is likely to correlate in part with the Hunnebergian Stage of Scandinavia. It was deposited probably in a largely stagnant basin, and records a shallowing-upwards sequence, prior to the Arenig transgression of the Stiperstones Quartzite. A sparse trilobite fauna proves the presence of theAngelina sedg vickiiBiozone, and a succeeding interval is characterized byAsaphelluscf.graffi. The trilobites are briefly described; they include the first undistorted material ofAngelina sedgwvickii. The brachiopodLingulella bella(Walcott), hitherto known only from eastern Newfoundland, is described by A. W. A. Rushton.
A fault-controlled depositional model for the Aberystwyth Grits turbidite system
Authors: Wilson D. , Davies J. R. , Waters R. A. , Zalasiewiczt J. A.
Published: May 2009

The Aberystwyth Grits Group was the first in a series of southerly-supplied sandstone-rich turbidite systems that invaded the Welsh Basin during the Telychian Stage (late Llandovery; Silurian). Structural and stratigraphical evidence indicates that deposition of the sand-dominated parts of the system was largely restricted to the east by a zone of syndepositional faulting, now marked by a major vergence divide. Downfaulting and reverse drag along the fault hangingwall created a bathymetric low, which focused deposition of high-density, sand-carrying turbidite flows and flow components, allowing substantial thicknesses of sediment to accumulate. In contrast, low-density, mud-rich turbidites were deposited over a wider area, enhancing the topographic relief generated by uplift above the fault footwall, to form a feature which restricted the spread of the coeval easterly-supplied turbidites of the Devil's Bridge Formation.
Petrogenesis of Ordovician igneous rocks in the southern part of the Welsh Basin
Authors: Bevins R. E. , Lees G. J. , Roacht R. A.
Published: May 2009

During early Ordovician times volcanic and high-level intrusive activity occurred at numerous centres across North Pembrokeshire. Previous work suggested a geochemical transition in this activity from calcalkaline through to tholeiitic with time. However, new data indicate more extensive calc-alkaline magmatism and that both magma types were coeval. The origin of the calcalkaline magmas remains equivocal, but the tholeiitic magmas appear to have been derived from a source similar to N-type MORB, variably modified by supra-subduction zone fluids, combined with some fractionation during ascent. These data are consistent with emplacement in a supra-subduction zone marginal basin.
Seismic reflection test on the granite of the Skye Tertiary igneous centre
Authors: Goulty N. R. , Leggett M. , Douglas T. , Emeleus C. H.
Published: May 2009

We have conducted a seismic reflection test over a short profile on the granite of the Skye Tertiary central intrusive complex. From previous gravity modelling work it had been inferred that the granite is approximately 1.5 km thick and overlies basic rocks. The seismic data indicate that the granite is at least 2 km thick at the test location. Reflection events of alternating polarity between depths of 2.1 and 2.4 km suggest that basic and acidic sheets are interlayered at the base of the granitic mass.
The origins of granulites: a metamorphic perspective
Authors: Harley S. L.
Published: May 2009

Although many recent reviews emphasize a uniformity in granulite pressure–temperature (P–T) conditions and paths, granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation. A thorough survey of over 90 granulite terranes or occurrences reveals that over 50% of them recordP–Tconditions outside the 7.5 ± 1 kbar and 800 ± 50 °C average granulite regime preferred by many authors. In particular, an increasing number of very high temperature (900−1000 °C) terranes are being recognized, both on the basis of distinctive mineral assemblages and geothermobarometry. Petrogenetic grid and geothermobarometric approaches to the determination and interpretation ofP–Thistories are both evaluated within the context of reaction textures to demonstrate that the large range inP–Tconditions is indeed real, and that both near-isothermal decompression (ITD) and near-isobaric cooling (IBC)P–Tpaths are important. Amphibolite–granulite transitions promoted by the passage of CO2-rich fluids, as observed in southern India and Sri Lanka, are exceptional and not representative of fluid-related processes in the majority of terranes. It is considered, on the contrary, that fluid-absent conditions are typical of most granulites at or near the time of their recorded thermal maxima.

ITD granulites are interpreted to have formed in crust thickened by collision, with magmatic additions being an important extra heat source. Erosion alone is not, however, considered to be the dominant post-collisional thinning process. Instead, the ITD paths are generated during more rapid thinning (1−2 mm/yr exposure) related to tectonic exhumation during moderate-rate or waning extension. IBC granulites may have formed in a variety of settings. Those which show anticlockwiseP–Thistories are interpreted to have formed in and beneath areas of voluminous magmatic accretion, with or without additional crustal extension. IBC granulites at shallow levels (< 5 kbar) may also be formed during extension of normal thickness crust, but deeper-level IBC requires more complex models. Many granulites exhibiting IBC at deep crustal levels may have formed in thickened crust which underwentveryrapid (5 mm/yr) extensional thinning subsequent to collision. It is suggested that the preservation of IBC paths rather than ITD paths in many granulites is primarily related to therateandtimescaleof extensional thinning of thickened crust, and that hybrid ITD to IBC paths should also be observed.

Most IBC granulites, and probably many ITD granulites, have not been exposed at the Earth's surface as a result of the tectonic episodes which produced them, but have resided in the middle and lower crust for long periods of time (100−2000 Ma) following these events. The eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation.
Late Proterozoic glacial carbonates in northeast Spitsbergen: new insights into the carbonate–tillite association
Authors: Fairchild I. J. , Hambrey M. J. , Spiro B. , Jefferson T. H.
Published: May 2009

Carbonate-rich glacial deposits from two discrete Vendian glacial periods are described. The older is represented by the 24–40 m thick Petrovbreen Member (E2) of the Elbobreen Formation which contains abundant detrital dolomite. Clasts in E2 and their possible source rocks have positive δ13C and negative δ18OPDBvalues. In contrast the carbonate mud-fraction of E2 sediments has different cathodoluminescence characteristics from clasts, slightly negative δ13C values, and higher Fe and Mn concentrations than clasts. Oxygen isotopes vary from −2.5 to +4.5‰PDB, thought to be related to various seawater–meltwater mixtures in the depositional environment. Preservation of information about glacial sedimentary environments is attributed to early diagenetic recrystallization forced by excess surface free energy (Ostwald's ripening) and coinciding with sulphate reduction.

The younger glaciation is represented by the Wilsonbreen Formation (170 m) which has a distinctive glaciolacustrine Middle Carbonate Member (W2). W2 contains precipitated periglacial carbonates (with high Mn/Fe ratio): both limestone (rhythmitic and stromatolitic) and dolostone (rhythmites, stromatolites and dolomite-rich sandstones) which are compared with carbonates in modern Antarctic lakes. Evaporitic environments for dolomitic sandstones and stromatolitic dolostones are indicated by heavy oxygen isotope values (up to + 10.5‰PDB), high Na concentration and evidence for dissolved evaporites. High Mn concentration in detrital dolostones in W2 is suggestive of syn-sedimentary dolomite recrystallization in freshwater diamictites and haematitic siltstones.

The carbonate–tillite association ultimately arises from the erosion of underlying carbonates which originated (in this case) under radically different climatic conditions. Glacial depositional waters then became carbonate-saturated as a result of dissolution of detrital carbonate. Massive recrystallization of glacially transported carbonate is proposed as a geologically significant process with considerable potential for palaeoenvironmental analysis. In glacial lakes carbonate precipitated in response to evaporation or photosynthesis. Carbonate precipitation as the result of seawater freezing, or in warm interglacial conditions, is not yet established. Oxygen isotope value are inconsistent (too heavy) with the presence of high-latitude meltwaters, implying that glaciation extended to low latitudes as proposed by Harland.
Caledonian nappe geometry in north-central Sweden and basin evolution on the Baltoscandian margin
Authors: Gayer Rodney A. , Greiling Reinhard O.
Published: May 2009

Structural analysis of the Lower Allochthon in the north-central Scandinavian Caledonides has allowed the construction of restorable cross-sections consistent with the development of a foreland-propagating linked thrust system. The internal geometry of an antiformal stack, the Njakafjäll duplex, within the Lower Allochthon demonstrates tectonic shortening of c. 50% and suggests an overall predeformational width for the Lower Allochthon in this area of at least c. 130 km, and possibly considerably greater if the buried trailing edge of the Lower Allochthon lies in a comparable position to that farther south in Tröndelag. These results, combined with a stratigraphic analysis of the imbricates within the Lower Allochthon and of the adjoining Autochthon and Middle Allochthon, indicate the development, from Proterozoic through Cambrian times, of two sedimentary basins on the c. 200 km wide continental margin of Baltica bordering the Iapetus Ocean. The basins were separated by a region of basement relief, the Børgefjell domain, above which a reduced sequence of Vendian to Cambrian rocks accumulated. This Børgefjell basement high, and the similar Njakafjäll basement high to the east, subsequently became the sites of antiformal stack development. It is argued that the frequent incorporation of basement into the thrust sheets, together with the thin sedimentary fill of these basins, compared with the much greater fill in basins to the south in Jämtland and to the north of Finnmark, implies major palaeogeographic changes along the Baltoscandian margin, possibly related to early rift geometries. The apparent lack of subsequent foreland basin development in north-central Scandinavia compared with areas to the south may indicate a deeper level of thrust detachment beneath the Middle Allochthon to the north, such that any foreland basin sediments have been removed in the hangingwall and subsequently eroded. An alternative possibility is a primary absence of foreland basin development that may relate to a differing response to thrust loading by continental lithosphere which had been variably thinned during the earlier rift regime.
Microfossils from silicified stromatolitic carbonates of the Upper Proterozoic Limestone-Dolomite 'Series', central East Greenland
Authors: Green J. W. , Knoll A. H. , Swett K.
Published: May 2009

Silicified flake conglomerates andin situstratiform stromatolites of the Upper Proterozoic (c.700–800 Ma) Limestone-Dolomite ‘Series’, central East Greenland, contain well preserved microfossils. Five stratigraphic horizons within the 1200 m succession contain microbial mat assemblages, providing a broad palaeontological representation of late Proterozoic peritidal mat communities. Comparison of assemblages demonstrates that the taxonomy and diversity of mat builder, dweller, and allochthonous populations all vary considerably within and among horizons. The primary mat builder in most assemblages isSiphonophycus inornatum, a sheath-forming prokaryote of probable but not unequivocally established cyanobacterial affinities. An unusual low diversity unit in Bed 17 is dominated by a different builder,Tenuofilum septatum, while a thin cryptalgal horizon in Bed 18 is built almost exclusively bySiphonophycus kestron.Although variable taphonomic histories contribute to observed assemblage variation, most differences within and among horizons appear to reflect the differential success or failure of individual microbial populations in colonizing different tidal flat microenvironments. Twenty-two taxa are recognized, of which two are described as new:Myxococcoides stragulescensn.sp. andScissilisphaera gradatan. sp.
Sedimentology and structure of the trench-slope to forearc basin transition in the Mesozoic of Alexander Island, Antarctica
Authors: Doubleday P. A. , Macdonald D. I. M. , Nell P. A. R.
Published: May 2009

The Mesozoic forearc of Alexander Island, Antarctica, is one of the few places in the world where the original stratigraphic relationship between a forearc basin and an accretionary complex is exposed. Newlydiscovered sedimentary rocks exposed at the western edge of the forearc basin fill (the Kimmeridgian–Albian Fossil Bluff Group) record the events associated with the basin formation. These strata are assigned to the newly defined Selene Nunatak Formation (?Bathonian) and Atoll Nunataks Formation (?Bathonian-Tithonian) within the Fossil Bluff Group.

The Selene Nunatak Formation contains variable thicknesses of conglomeratesand sandstones, predominantly derived from the LeMay Group accretionary complex upon which it is unconformable. The formation marks emergence and subsequent erosion of the inner forearc area. It is conformably overlain by the1 km thick Atoll Nunataks Formation, characterized by thinly-bedded mudstones and silty mudstones representing a marine transgression followed by trench-slope deposition. The Atoll Nunataks Formation marks a phase of subsidence, possibly in response to tectonic events in the accretionary prism that are known to have occurred at about the same time.

The Atoll Nunataks Formation is conformably overlain by the Himalia Ridge Formation, a thick sequence of basin-wide arc-derived conglomerates. This transition from fine- to coarse-grained deposition suggests that a well-developed depositional trough (and hence trench-slope break) had formed by that time. The Atoll Nunataks Formation therefore spans the formation of the forearc basin, and marks the transition from trench-slope to forearc basin deposition.
Lower Palaeozoic and Precambrian igneous rocks from eastern England, and their bearing on late Ordovician closure of the Tornquist Sea: constraints from U-Pb and Nd isotopes
Authors: Noble S. R. , Tucker R. D. , Pharaoh T. C.
Published: May 2009

The U-Pb isotope ages and Nd isotope characteristics of asuite of igneous rocks from the basement of eastern England show that Ordovician calc-alkaline igneous rocks are tectonically interleaved with late Precambrian volcanic rocks distinct from Precambrian rocks exposed in southern Britain. New U-Pb ages for the North Creake tuff (zircon, 449±13 Ma), Moorby Microgranite (zircon, 457 ± 20 Ma), and the Nuneaton lamprophyre (zircon and baddeleyite, 442 ± 3 Ma) confirm the presence ofan Ordovician magmatic arc. Tectonically interleaved Precambrian volcanic rocks within this arc are verified by new U-Pb zircon ages for tuffs at Glinton (612 ± 21 Ma) and Orton (616 ± 6 Ma). Initial εNd values for these basement rocks range from +4 to - 6, consistent with generation of both c. 615 Ma and c. 450 Ma groups of rocksin continental arc settings. The U-Pb and Sm-Nd isotope data support arguments for an Ordovician fold/thrust belt extending from England to Belgium, and that the Ordovician calc-alkaline rocks formed in response to subductionof Tornquist Sea oceanic crust beneath Avalonia.
Mid-Turonian ammonite faunas from northern Mexico
Authors: Kennedy W. J. , Cobban W. A.
Published: May 2009

Turonian ammonite assemblages are described from six localities in the Ojinaga and Boquillas formations of Chihuahua in northern Mexico. These assemblages reveal the presence of the middle Turonian zones of Collignoniceras woollgari and Prionocyclus hyatti far to the south of previously documented occurrences. The Mexican collections include co-occurring collignoniceratids, known from as far north as Montana, and Tethyan euomphaloceratines and coilopoceratids. One species, Puzosia (Puzosia) serratocarinata, is new.
Maastrichtian ammonites from the Corsicana Formation in northeast Texas
Authors: Kennedy W. J. , Cobban W. A.
Published: May 2009

Previously undescribed collections of ammonites from the Corsicana Formation (Maastrichtian), the highest unit of the Cretaceous present in northeast Texas, U.S.A., includeEubaculites carinatus(Morton, 1834),Nostoceras (Nostoceras) majorsp. nov.,Glyptoxocerassp., andJeletzkytessp. nov., which are new records for the unit. Other ammonites areSphenodiscus lobatus(Tuomey, 1854),S. pleurisepta(Conrad, 1857),Trachyscaphites yorkensis(Stephenson, 1941),Discoscaphites conradi(Morton, 1834) andBaculites columna(Morton, 1834). Elements of the fauna are present in the Escondido Formation in Trans-Pecos Texas and northern Mexico, the Prairie Bluff Chalk in Alabama and Mississippi, the Owl Creek Formation in Mississippi, Tennessee and Missouri, and the Severn Formation in Maryland. In the U.S. Western Interior they occur in theHoploscaphites nicolletiZone, in the Fox Hills Formation.
Late Mesozoic bipolar bivalve faunas
Authors: Crame J. A.
Published: May 2009

Bipolar bivalve genera probably existed through the greater part of late Mesozoic (i.e. late Jurassic–late Cretaceous) time. Of the various theories put forward to account for their presence, those based on some form of global climatic zonation seem most appropriate. Although equatorial–polar temperature gradients were substantially less in late Mesozoic time than at the present day, high latitude regions were subjected to temperate (or even cool-temperate) climatic regimes. Macrobenthonic marine faunas may have been more susceptible to differentiation in response to these climatic patterns than nektonic ones. This is particularly so in the late Mesozoic strata of the Southern Hemisphere.
Devonian Antiarch Biostratigraphy of China
Authors: Kiang P'an
Published: May 2009

Devonian Antiarchi in China are chiefly distributed in the S and W of the country. They are represented by 17 genera and more than 26 species, of which three genera are cosmopolitan, namely Asterolepis, Bothriolepis and Remigolepis. The early Devonian Antiarchi fauna, Yunnanolepis, Phymolepis, Zhanjilepis, is an East Asiatic fauna. The middle and late Devonian faunas are essentially endemic and associated with few cosmopolitan elements, their geological ages, however, are different from those of the cosmopolitan antiarch taxa elsewhere. As considered in the present study, six main antiarch assemblages occur: (1) Yunnanolepis-Qujinolepis assemblage (Lower Devonian), (2) Xichonolepis-Wudinolepis assemblage (Eifelian), (3) Hunanolepis tieni-Bothriolepis sinensis assemblage (Givetian), (4) Bothriolepis kwangtungensis-Bothriolepis lochangensis assemblage (Givetian), (5) Remigolepis spp. assemblages (Frasnian-Famennian), (6) Sinolepis-Asterolepis sinensis assemblage (Famennian).
A reappraisal of the conditions of deposition of the Maentwrog Beds (Upper Cambrian) at Porth Ceiriad, North Wales
Authors: Bose P. K.
Published: May 2009

The marine Maentwrog Beds comprise a repetition of sand and mud facies and follow a non-sequence. A shallow water depositional environment is inferred from the nature of the basal unit (with stromatolites and intraformational conglomerate), and hummocky cross-stratification and mud-draped erosion surfaces. The bulk of the formation was deposited between fair weather and storm wave base, the sand facies representing storm depositional events.
Potassium-argon ages from Tristan da Cunha, South Atlantic
Authors: McDougall Ian , Ollier C. D.
Published: May 2009

Potassium-argon ages measured on 11 volcanic rocks, mainly lavas, from Tristan da Cunha range from 0.21 ± 0.01 to 0.01 ± 0.02 Ma, and confirm the youthfulness of this volcano, which lies on the Walvis Ridge just to the east of the crest of the Mid Atlantic Ridge.