bluuebunny/crossref_metadata_2025_split huggingface dataset:
The geological significance of some Triassic microfossils from the South Orkney Islands, Scotia Ridge
Authors: Dalziel I. W. D. , Elliot D. H. , Jones D. L. , Thomson J. W. , Thomson M. R. A. , Wells N. A. , Zinsmeister W. J. 
Published: May 2009

SummaryLate Triassic Radiolaria have been recovered from a bedded chert collected early in 1977 in the South Orkney islands. This is the first reliable palaeontological evidence for the age of the so-called basement complex that forms most of the exposed rock of a microcontinent on the southern limb of the Scotia Ridge. The fossils place a lower limit on the age of deformation of at least part of the complex as post-Karnian or Norian. The basement is overlain by undeformed Jurassic to Cretaceous conglomerates, which suggests this event took place during the early Mesozoic Gondwanian orogeny.The new data are consistent with the interpretation that the basement complex of the South Orkney Islands represents part of a subduction complex and was accreted to the Pacific margin of Gondwanaland during the late Triassic or early Jurassic time.
The application of trend surface analysis to directional data
Authors: Shakesby R. A. 
Published: May 2009

SummaryTrend surface analysis has been used widely in geology and geomorphology but only rarely has it been applied to directional data. This neglect stems from the inapplicability of normal trend surface procedures to such data. An adaptation of normal trend surface procedures specifically designed for use with directional data is, however, available as a FORTRAN IV computer program. This technique is described and its usefulness in generalizing regional patterns of flow is illustrated by applying it to data representing ice flow direction in Central Scotland.
Quartz-albite rocks of ash-fall origin
Authors: Leitch Evan C. 
Published: May 2009

SummaryThin beds composed mainly of quartz and albite occur interstratified with epiclastic rocks in a thick marine Early Permian sequence in the eastern part of the New England Fold Belt, eastern Australia. The sequence has suffered very low grade regional metamorphism and the quartz-albite rocks retain few primary textural features. A pyroclastic origin for these rocks is argued on the basis of inherited sedimentary characters and their distinctive mineralogical and chemical composition, and it is suggested that they accumulated as glass-rich ash-fall tuffs. The present chemical composition of the quartz-albite rocks suggests the tuffs may have initially altered to zeolitic assemblages. Similar quartz-albite rocks, perhaps misidentified as chert or siliceous siltstone, probably occur in other low-grade metamorphic sequences, the progenitors of which accumulated adjacent to active magmatic arcs.
The Ordovician proetacean trilobiteRorringtonia
Authors: Owens R. M. 
Published: May 2009

SummaryNew, well-preserved material of the Ordovician proetacean trilobiteRorringtonia, hitherto of uncertain taxonomic position, indicates that it belongs to the aulacopleurid subfamily Scharyiinae. It also elucidates the position of another problematic proetacean,Analocaspis, which is now considered to be congeneric withRorringtonia.
Irumide and post-Mozambiquian plutonism in Malawi
Authors: Haslam H. W. , Brewer M. S. , Darbyshire D. P. F. , Davis A. E. 
Published: May 2009

SummaryRb-Sr whole-rock isochron ages of 443 ± 30 Ma, 449 ± 42 Ma and 489 ± 14 Ma with initial 87Sr/86Sr ratios of 0.70669 ± 0.00068, 0.70599 ± 0.00035 and 0.70658 ± 0.00025 were obtained, respectively, for the Cape Maclear granite, the surrounding Cape Maclear syenite and the Senga Bay granitic body. The results confirm previous estimates of the age of the post-Mozambiquian Lake Malawi Granitic Province, of which these plutons are part. Data from the Dzalanyama granite have excess scatter, but indicate an Irumide age of about 1000 Ma. This batholith is therefore much older than the Lake Malawi Granitic Province but much younger than the Nyika granite of northern Malawi, contrary to earlier suggestions. The porphyritic foliated granite of Mcezi Hill gave an age of 1016 ± 55 Ma and an initial ratio of 0.70522 ± 0.00084. Irumide plutonism in the region includes several dissimilar groups of intrusions, all with low initial87Sr/86Sr ratios. The Irumide age of the Dzalanyama granite makes it possible that the metasediments of the Mchinji Group are wholly post-Ubendian.
Partial melting of semipelite and the development of marginal breccias around a late Caledonian minor intrusion in the Grampian Highlands of Scotland
Authors: Platten I. M. 
Published: May 2009

SummaryA water saturated melt was developed in the semipelitic Leven Schist in contact with the kentallenitic basic rocks of the Barnamuc intrusion. The partly melted rock consisted of a small volume of granitic melt with relict refractory quartz grains and layers of aluminosilicates. This material could be mobilized and mixed with phenocryst-bearing magma. Sheets of country rock breccia are associated with the mobilization and veins of breccia and mobilized hornfels invade the intrusion. Sheets of igneous rock occur along the contact zone and their emplacement is related to the mobilization of the hornfels. Loss of cohesion between solid country rock and crystallized outer parts of the plug leads to collapse and removal of early formed igneous rocks, accounting for the lack of chilled margins in some intrusions.
The double cone fracture in flint
Authors: Williams D. J. 
Published: May 2009

SummaryThis work proposes a mechanism for the formation of the characteristic ‘double cone’ cracking and ‘bulb of percussion with bulbar scar’ cracking caused by the artificial fracture of flint. The double cone fracture is observed as a large, small apex angle, cone that is truncated by a smaller cone of increased apex angle. The author considers that the large narrow apex angle truncated cone of the fracture is caused by Hertzian loading of the flint on impact and the upper complete cone is formed as a result of the unloading of the stressed flint. This mechanism has been deduced from work carried out in the fractography of glass by others and from some restricted laboratory experiments.
Tremadoc faunas from the Carmarthen district, South Wales
Authors: Owens R. M. , Fortey R. A. , Cope J. C. W. , Rushton A. W. A. , Bassett M. G. 
Published: May 2009

SummaryA diverse fauna of trilobites, graptolites, inarticulate brachiopods, sponges, and a worm is described from the Tremadoc rocks cropping out in the Llangynog district, SW of Carmarthen. It permits identification of theClonograptus tenellusZone and older Tremadoc strata; younger Tremadoc strata are apparently absent. The fauna shows closest affinities with the Shineton Shales of Shropshire, while some of the trilobites also indicate a close relationship with those from the Tremadoc of NW Argentina.
Calymene quadrata King, 1923 and allied species of trilobites from the Ashgill Series of North Wales
Authors: Price David 
Published: May 2009

SummaryCalymene quadrata King is re-described. Two new species of similar age and provenance are erected and considered to be closely allied to quadrata; all three forms are thought to be best placed in genus Gravicalymene Shirley. G. pontilis sp.nov., the stratigraphically oldest form suggests derivation of the group from an ancestor such as G. deani Ingham. G. arcuata sp.nov. is the youngest form. Variation in the preglabellar area between the three forms argues for an expansion of the diagnosis of genus Gravicalymene; this would allow it to contain forms previously placed in genus Sthenarocalymene Siveter.
New Arctocephalitinae (Ammonoidea) from the Middle Jurassic of Kong Karls Land, Svalbard
Authors: Rawson P. F. 
Published: May 2009

SummaryCostacadoceras bluethgeni gen. et sp.nov. and Articoceras harlandi sp.nov. are described from the base of the Kongsøya Formation of Kong Karls Land, Svalbard, and dated as mid boreal Bathonian (early ishmae Zone).
Fission-track dating of British Ordovician and Silurian stratotypes
Authors: Ross R. J. , Naeser C. W. , Izett G. A. , Obradovich J. D. , Bassett M. G. , Hughes C. P. , Cocks L. R. M. , Dean W. T. , Ingham J. K. , Jenkins C. J. , Rickards R. B. , Sheldon P. R. , Toghill P. , Whittington H. B. , Zalasiewicz J. 
Published: May 2009

SummaryFission-track dating of zircons and apatites from tuffs and bentonites has produced the first isotopic ages for the type sections of the Ordovician and Silurian Systems. In the Ordovician the following ages have been determined: lower Arenig 493 Ma, lower Llanvirn 487 Ma, lower Llandeilo 477 Ma, upper Caradoc 463 Ma and upper Ashgill 434 Ma. In the Silurian, the following: lower Llandovery 437 Ma, lower Wenlock 422 Ma, upper Wenlock 414 Ma and Ludlow 407 Ma. The Ordovician-Silurian boundary is interpreted as occurring at about 436 Ma. Three North American Rocklandian bentonites yielded zircons whose ages average 453 Ma. This is about 10 Ma younger than supposedly correlative units in the British type sections.
Rift and thrust tectonics associated with a translational block slide, Abbotsford, New Zealand
Authors: Bishop D. G. , Norris R. J. 
Published: May 2009

AbstractThe East Abbotsford translational block landslide failed suddenly on 8 August, 1979, after months and probably years of slowly accelerating movement. A displacement of about 50 m occurred on a bedding plane dipping 7°, about 30 m below ground surface, at or very near the contact between two formations.The complex graben formed around the head of the landslide is a small scale example of extensional (rift) tectonics. A wedge and prism model is developed to fit the geometry, and meet the constraints of preserving the cross-sectional area and stratal length of the beds involved and also to account for the sequential retrogressive failures of the trailing edge of the sliding block.Reconstruction of the failure sequence at the toe shows the compressional zone to be dominated by overthrusting on upward sloping surfaces or ramps, with subsidiary backthrusting and buckling.The energy expended in overthrusting, coupled with the decrease in mass (and hence driving force) resulting from the retrogressive spalling of the trailing edge of the slide block, indicates that the phase of rapid movement was accompanied by a sudden decrease in resistance on the failure surface for a movement of 50 m to have occurred.Both the rift and thrust structures associated with the landslide have large scale tectonic analogues.
Gas filter-pressing origin for segregation vesicles in dykes
Authors: Sanders I. S. 
Published: May 2009

AbstractSegregation vesicles have been recognized in two plagiophyric dolerite dykes in northwestern Ireland. The vesicles are each outlined by a rim of tangentially arranged plagioclase, and filled to a variable extent by a fine-grained, crescent-shaped lining of fractionated residual melt. They closely resemble segregation vesicles reported from Atlantic ocean-floor basalts.It is suggested (1) that the vesicles began as CO2-rich bubbles released during decompression; (2) that these bubbles grew very little during crystallization, while H2O became concentrated in the residual melt; and (3) that exsolution and expansion of H2O-rich vapour forced interstitial residual melt through the rigid but permeable framework of crystals and into the existing CO2-rich bubble cavities.
K—Ar ages of alkaline igneous rocks in the northern Oman mountains, NE Arabia, and their relations to rifting, passive margin development and destruction of the Oman Tethys
Authors: Lippard S. J. , Rex D. C. 
Published: May 2009

SummaryK–Ar ages of biotites from a variety of alkaline volcanics and minor intrusive rocks in the nothern Oman mountains allochthon give a range of ages from Triassic (230 Ma) to mid Cretaceous (92 Ma) and represent igneous activity on the Oman continental margin throughout the Mesozoic. This was a passive margin destroyed by the emplacement across it of a pile of nappes in the late Cretaceous, including a largely intact thrust sheet of Upper Cretaceous oceanic lithosphere (the Semail ophiolite). Biotite ankaramite dykes, cutting compositionally similar volcanics, in the thrust complex immediately beneath the ophiolite, give Triassic ages and are related to the rifting and break-up of the northeast Arabian margin at the beginning of formation of the Oman Tethys. Mid Cretaceous (Cenomanian–Turonian) ages are mostly recorded from the northern part of the mountains where there are alkaline tuffs in a sedimentary melange. They are approximately the same age as the ophiolite and may be related to tectonic instability of the Oman margin immediately prior to ophiolite emplacement. Alkaline sills, intrusive into a variety of rocks, including Triassic volcanics, give Jurassic and Cretaceous ages and are interpreted as periodic alkaline activity on the Oman margin throughout passive margin development.
An analysis of the molluscs from an Ipswichian interglacial river channel deposit at Maxey, Cambridgeshire, England
Authors: French C. A. I. 
Published: May 2009

SummaryA freshwater and land molluscan assemblage from an Ipswichian stream channel at Maxey, Cambridgeshire, is discussed. The presence of Belgrandia marginata and Vallonia enniensis suggests that summer temperatures may have been somewhat warmer in the Ipswichian period. The assemblage represents the silting processes under relatively quiet water conditions, possibly in a side channel or backwater of a meandering river system.
Outflow ignimbrite sheets from Late Carboniferous calderas, Currabubula Formation, New South Wales, Australia
Authors: McPhie J. 
Published: May 2009

SummaryRegionally mappable, silicic, outflow ignimbrite sheets are interbedded with fluvial volcanogenic conglomerates and sandstones of the Late Carboniferous Currabubula Formation of north-eastern N.S.W. Four of the most widespread of these ignimbrites are described and defined as members. The oldest member is comprised of many thin, originally non-welded flow units. Interbedded accretionary lapilli horizons may indicate phreatomagmatic activity at vent during the eruption in addition to local rain-flushing of co-ignimbrite ash clouds. Of the three other members, two are multiple flow-unit sheets, 160–180 m in aggregate thickness. Substantial portions of these sheets were originally welded. The remaining member is a simple welded ignimbrite characterized by abundant spherulites and lithophysae. Irregular pre-eruption topography and contemporaneous erosion were responsible for thickness variations of the ignimbrite sheets. Some palaeovalleys, now delineated by the ignimbrites, persisted in spite of repeated pyroclastic influxes. Relic pumice, shards and crystal fragments are ubiquitous components of the sedimentary facies of the Currabubula Formation, and were probably derived from originally poorly consolidated pyroclastic deposits such as airfall ash layers and non-welded ignimbrites. No surface trace of the sources of these ignimbrites exists. However, internal facies, thickness variations and volumes of the ignimbrites indicate that they periodically emanated from a multiple-caldera terrain which was continuously active during the Late Carboniferous, and located several kilometres to the west of present exposures.
The chronometric age of the Sinian–Cambrian boundary in the Yangtze Platform, China
Authors: Zichao Zhang , Guogan Ma , Huaqin Lee 
Published: May 2009

AbstractThe Cambrian and Precambrian sedimentary strata in the centre and west part of the Yangtze Platform are in continuous successions, in which the Tiantzushan Member and the Meisuchun Formation are exceedingly rich in shelly fossils. In Co-operation with the stratigraphic study in depth and in order to determine the isotopic age for the Precambrian–Cambrian boundary in the Yangtze Platform, a number of isotopic age determinations by different techniques have been made in the laboratories of the Yichang Institute of Geology and Mineral Resources and the Research School of Earth Sciences, Australian National University, mainly on the sequences in the Yangtze Gorges area together with those from some other areas in the Yangtze Platform. In this paper, the authors summarize all of these results and infer 610±10 Ma as an age for the Sinian–Cambrian Boundary in the Yangtze Platform if the ‘golden spike’ is considered to be placed at the bottom of the Meishucun Stage.
Box-fault systems and ramps: atypical associations of structures from the eastern shoulder of the Kenya Rift
Authors: Griffiths P. S. 
Published: May 2009

SummaryBox-fault systems are striking arrangements of short faults that are associated with complex groups of elongate, tilted fault blocks (ramps). They occur within the faulted eastern shoulder of the Rift Valley, close to the equatorial bend in its alignment. This association of small-scale structures is shown to be integrated within the large-scale, asymmetrical structural pattern of the equatorial bend.
The pelvis of Archaeopteryx
Authors: Walker A. D. 
Published: May 2009

SummaryExamination of the Eichstätt specimen of Archaeopteryx shows that the pubis agrees with those of the Berlin and London specimens in indicating a downward and backward inclination of some 135° relative to a line drawn through the lower extremities of the iliac blade. The greater part of the backward rotation of the bird pubis had thus taken place by the Kimmeridgian Stage (sensu anglico) of the Upper Jurassic. A definite pectineal process is present in Archaeopteryx, indicating the existence of a well-developed ambiens muscle. Some preliminary remarks are made about the skull of Archaeopteryx.
A palaeomagnetic analysis of Miocene fluvial sediments at Pertusa, near Huesca, Ebro Basin, Spain
Authors: Turner P. , Hirst J. P. P. , Friend P. F. 
Published: May 2009

AbstractIn the Miocene fluvial system of the Huesca area, in the Ebro Basin, northern Spain, rivers radiated outwards, to the south and west, from a small sector of the northern margin of the basin. The deposits of the system extend about 60 km radially from this sector and then pass into calcareous and gypsiferous deposits.The magnetostratigraphy of two logged sections, 1 km apart, within this system consists of an upper zone of normal polarity and a lower zone of reversed polarity. The lithostratigraphy and magnetostratigraphy are parallel.The sands and silts are dominated by angular quartz, intraformational clay lithograins and calcite lithograins. They are mainly pale yellow brown to dusky yellow, and magnetic tests indicate that the magnetization is carried dominantly by ferric oxyhydroxides (haematite and gôethite). The higher temperature Natural Remanent Magnetization is probably due to detrital haematite which would have been partially aligned during fluvial deposition. Post-depositional modification (PDRM) may have occurred during dewatering.Haematite pseudomorphing pyrite framboids indicates that early reducing conditions were succeeded by a more oxidizing regime which produced secondary magnetizations associated with fine-grained haematite and goethite.Complete polarity zones are not delineated, but the thicknesses present are not excessive compared with other continental Miocene deposits. The average palaeolatitude of 22° is lower than would be expected for the Miocene of northern Spain, probably due to incomplete averaging of secular variations and other sources of error including possible ‘inclination error’.
Upper Cambrian Archaeocyatha from Antarctica
Authors: Debrenne F. , Rozanov A. Yu. , Webers G. F. 
Published: May 2009

AbstractReconnaissance geological mapping (1962–75) followed by detailed geological investigations (1979–80) in the Ellsworth Mountains of west Antarctica have established the existence of extensive Middle and Late Cambrian strata. Forms tentatively referred to Archaeocyatha have been examined by F.D. and A.R., who concluded that, despite the commonly held opinion that the phylum became extinct at the boundary of the Lower and Middle Cambrian, the Ellsworth Mountains' forms represented Irregularian Archaeocyatha which survived in protected niches into the Late Cambrian. The age of the fauna containing the archaeocyaths is firmly dated by abundant trilobites including species of Homagnostus, Pseudagnostus, Kormagnostella, Erixanium and Onchopeltis.
Lower Palaeozoic convergent plate margin volcanism on Bømlo, southwest Norwegian Caledonides: geochemistry and petrogenesis
Authors: Furnes Harald , Brekke Harald , Nordås Jan , Hertogen Jan 
Published: May 2009

AbstractMajor and trace element analyses of a Lower Palaeozoic metavolcanic sequence of convergent plate type from Bømlo, southwest Norwegian Caledonides, are presented and discussed. This sequence ranges in age from the Upper Cambrian through the Lower Silurian. Petrogenetic models for the lavas in terms of partial melting and crystal fractionation are discussed. Two models are presented for the metabasalts in order to explain their different trace element abundances and ratios:(1) REE modelling, assuming a mantle source with REE abundances twice chondritic, suggests progressively more varied sources with time. Thus the metabasalts from the oldest (Upper Cambrian–Lower Ordovician) Geitung Unit of primitive island arc type, and those of the mid-Ordovician Siggjo Complex of ‘Basin and Range’ type can be modelled in terms of high (around 25%) and moderate (around 5%) degrees of partial melting of spinel lherzolite, respectively. The metabasalts of the post-Ashgillian Vikafjord Group of typical continental flood basalts are compatible with moderate (c. 5–10%) degrees of partial melting of spinel- and garnet-lherzolite sources. The supposed Lower Silurian Langevåg Group of calc-alkaline ‘Andean’ type metabasalts, grading into alkaline to tholeiitic metabasalts of early marginal basin (youngest) character, require low (<5%) to moderate degrees of partial melting of amphibole-, garnet- and spinel-lherzolite sources, respectively.(2) Source heterogeneity, produced by subduction zone-derived enrichment of LIL elements, and contemporaneous stabilization of minor phases which accommodate HFS elements. This process, combined with possible continental contamination, may possibly yield the trace element concentrations and ratios of the different metabasalts by partial melting of modally similar mantle sources.
A review of the tectonics of the northern Middle East region
Authors: Lovelock P. E. R. 
Published: May 2009

AbstractThe structure of the northern part of the Arabian platform is reviewed in the light of hitherto unpublished exploration data and the presently accepted kinematic model of plate motion in the region. The Palmyra and Sinjar zones share a common history of development involving two stages of rifting, one in the Triassic–Jurassic and the other during late Cretaceous to early Tertiary times. Deformation of the Palmyra zone during the Mio-Pliocene is attributed to north–south compression on the eastern block of the Dead Sea transcurrent system which occurred after continental collision in the north in southeast Turkey. The asymmetry of the Palmyra zone is believed to result from northward underthrusting along the southern boundary facilitated by the presence of shallow Triassic evaporites. An important NW-SE cross-plate shear zone has been identified, which can be traced for 600 km and which controls the course of the River Euphrates over long distances in Syria and Iraq. Transcurrent motion along this zone resulted in the formation of narrow grabens during the late Cretaceous which were compressed during the Mio-Pliocene. To a large extent, present day structures in the region result from compressional reactivation of old lineaments within the Arabian plate by the transcurrent motion of the Dead Sea fault zone and subsequent continental collision.
Devonian brachiopod biostratigraphy of China
Authors: Hong-Fei Hou 
Published: May 2009

SummaryTwo Devonian biogeographic provinces are recognised in China, based on brachiopod distribution. The Junggar-Xinan Province to the north shows a mixture of European and North American elements, but notably no stringocephalids are present. The South China Province, which is subdivided into three subprovinces possesses more elements of European type.