bluuebunny/crossref_metadata_2025 huggingface dataset:
Late quaternary explosive silicic volcanism on St Lucia, West Indies
Authors: Wright J. V. , Roobol M. J. , Smith A. L. , Sparks R. S. J. , Brazier S. A. , Rose W. I. , Sigurdsson H.
Published: May 2009

Many explosive eruptions of dacitic magmas have occurred on St Lucia during the late Quaternary. These have produced widespread aprons and fans of pumice flow and ash flow deposits radiating around the central highlands, with co-eruptive air-fall and surge layers interbedded with palaeosols and epiclastic deposits. Vents in the highlands have not been located because of the dense tropical jungle but we suspect they are now plugged by lava domes surrounded by aprons of block and ash flow deposits. Young magmatically related dacitic lava domes have been extruded in the Qualibou depression. The pumice succession can be divided into older quartz-poor deposits forming the Choiseul Pumice and younger crystal-rich deposits with abundant large quartz which are called the Belfond Pumice. The Choiseul Pumice groups together scattered remnants of the products of many eruptions of different low-silica dacitic magma types. The Belfond Pumice is the product of several eruptions of a high-silica magma type and 14C ages have dated these between 20900 to 34200 years B.P.

The pumice flow deposits occur as small-volume valley fills. A granulometric study of Belfond pumice flow deposits shows them to be strongly depleted in finer ash and vitric components. It is suggested that the narrow, winding and vegetated valleys on the island locally induced turbulence and the flows moved with large, highly fluidized and inflated heads, resulting in substantial loss of fine vitric ash. One ash flow deposit which is extremely rich in crystals and carbonized vegetation is highly depleted in fines and shows enhanced vitric losses. This flow may have been a much more violent ash hurricane or blast which surmounted topography ingesting large amounts of lush vegetation. Ignition of this released the large quantities of gas needed to elutriate most of the fines.

A model is suggested for the recent volcanic activity on St Lucia in which separate batches of silicic magma, each having a distinctive petrological and chemical character, rose into high level chambers over a large area. Eruptions of volatile-rich magma led to highly explosive pumice-forming activity from vents in the central highlands. Degassed and more crystal-rich magma was extruded later from the same vents or in the attenuated flank of the Qualibou depression to from lava dome complexes.
Re-interpreting ‘segmented’ grain-size curves
Authors: Christiansen C. , Blæsild P. , Dalsgaard K.
Published: May 2009

Cumulative curves of grain-size against frequency often show segmented shapes. These shapes have been interpreted as resulting from a combination of normally distributed populations each of which should reflect a mode of transport. The present study deals with samples in motion as bedload, pure saltation load and suspended load. All of these exhibited segmented shapes on cumulative curves. An explanation of this is that the populations are better described as log-hyperbolic distributions rather than as a mixture of log-normal distributions. The log-hyperbolic distribution when plotted on probability paper has a shape which can be misinterpreted as consisting of segments.
Precambrian–Cambrian boundary candidate, Meishucun, Jinning, Yunnan, China
Authors: Yusheng Xing , Huilin Luo
Published: May 2009

Being located in Jinning County, Yunnan Province, approximately 103°E, 25°N, the Meishucun section has a long history of study, convenient accessibility, mild spring-like climate all the year round and good exposures of the relevant strata. In the particular area there occur monofacial transitional carbonate deposits of marine origin, yielding in great abundance both small shelly fossils and trace fossils, which are present in close association and in some cases on the same bedding surface. The sequence of biotic assemblages is clearly evident and can be used for wide intercontinental correlation.

In the lower part of the Qiongzhusi Stage, stratigraphically higher, there appear the oldest trilobites, archaeostracods andBaltisphaeridiumcharacteristic of the Early Cambrian.

During the last six years great progress has been made in the study of the particular section through lithostratigraphic, biostratigraphic, geochronological, magnetostratigraphic and seismostratigraphic approaches, thus making the Meischucun Stage and the Sinian–Cambrian boundary stratotype section in the Meishucun area a Chinese candidate for global stratotype section and point for the Precambrian–Cambrian boundary.
Global distribution of the earliest shelly metazoans
Authors: Zhiwen Jiang
Published: May 2009

abstract

The appearance of the first abundant skeletal organisms in the earliest Cambrian was a quantum leap in the evolutionary history of life. It provided the foundations of the animal kingdom from Cambrian times onwards. This paper demonstrates that this evolutionary process resulted from a combination of environmental and biological factors. The author maintains that the appearance of the oldest shelly fossils is a reasonable criterion for defining the Precambrian–Cambrian boundary. This arises not only from the viewpoint of taking the Cambrian Period as the first period in the Palaeozoic Era, but is also a logical extension of regarding the history of life as being divisible into a series of developmental stages.
Mass flow deposits on a mid-Tertiary carbonate shelf, southern New Zealand
Authors: Hyden Fiona M.
Published: May 2009

Sheet-like and channel-filling conglomerates and pebbly biomicrudites occur within a sequence of cross-stratified shallow-water bioclastic limestones, the Forest Hill Formation of Late Oligocene to Early Miocene age. The largest channel, 50 m wide, 9 m deep, and at least 1.2 km long, is infilled with four separate conglomerate units of pebble- to boulder-sized limestone lithoclasts in a sparse muddy matrix (biomicrudite). Both the conglomerates and associated pebbly biomicrudites possess features characteristic of high concentration mass flows - both of laminar flow (preferred clast orientation, inverse grading or massive bedding) and of turbulent flow (normal coarse-tail or distribution grading and stratification). Clast imbrication (a- or b-axes) is suggestive of gradual deposition. Some flows travelled far enough to allow both vertical and horizontal differentiation of the coarse sediment. Facies models which have been proposed for conglomerates of deep water (turbidite) association can also be applied to the small-scale neritic conglomerates. Formation and remobilisation of such coarse grained facies in a shelf setting is attributed to eustatic sea-level changes and/or to local tectonism.
The volcanological significance of deep-sea ash layers associated with ignimbrites
Authors: Sparks R. S. J. , Huang T. C.
Published: May 2009

Many volcanic ash layers preserved in deep-sea sediments are the products of large magnitude ignimbrite eruptions. The characteristics of such co-ignimbrite ash-fall deposits are illustrated by two layers from the Eastern Mediterranean: the Minoan ash, Santorini, and the Campanian ash, Italy. These layers are divisible into a coarse lower unit and a fine upper unit in proximal cores. Both layers also show striking bimodal grain size distributions in more distal cores. The coarser mode decreases in median diameter with distance from source whereas the finer mode shows no lateral variation. These features are interpreted in terms of a model for ignimbrite formation by eruption column collapse. Comparable volumes of ignimbrite and associated air-fall ejecta are produced.
Reading segmented grain-size curves
Authors: Walton E. K. , Stephens W. E. , Shawa M. S.
Published: May 2009

Cumulative curves of grain-size against frequency often show segmented shapes which have been interpreted as the result of combination of normally distributed populations. The origin of the segments is explored by the examination of two classes of models, truncation and mixing. Similar curves may be generated by a variety of models. The segments rarely reflect precisely the original populations. Simulation of the tri-segmented curves commonly ascribed to combinations of suspension, saltation and traction populations shows that the characteristics of the contributing populations are not consistent with these three modes of transportation.
Early Miocene extrusives and shallow intrusives from Small Nggela, Solomon Islands
Authors: Plimer I. R. , Neef G.
Published: May 2009

Chemically similar altered gabbro, tholeiitic basalt, basaltic andesite and calc-alkaline rhyolite of Early Miocene age is present on Small Nggela, Solomon Islands. Large vesicles are invariably lacking from the autochthonous basaltic pillow lava which has narrow chilled margins, but clasts of allochthonous basalt present in coeval Early Miocene sediment are commonly vesicular. This suggests that the autochthonous lava was deposited in deep water (> 2.5 km) whereas the allochthonous lava was formed upslope in shallow water. A progressive increase in the tholeiite in Zr, Ti, K2O/(K2O+Na2O), Rb/Sr and K2O/Rb from N to S confirms that an Early Miocene southward-descending subduction zone, postulated by some authors, was present. Its recognition implies that the subduction zone did not migrate far during the Early Miocene.
A tholeiitic andesite flow unit among the Causeway Basalts of North Antrim in Northern Ireland
Authors: Francis P. E. , Lyle P. , Preston J.
Published: May 2009

A tholeiitic andesite flow unit occurs in tholeiitic basalt lava in the Giant's Causeway region of North Antrim, Northern Ireland. It is the first example of an intermediate differentiate to be found among these quartz-normative basalts. Separate magma batches for the preceding and succeeding basalt formations are indicated by their Zr/P2O5 ratios, and by the differing fractionation trends shown by molecular proportion ratio plots. The tholeiitic andesite was probably extruded in a superheated condition with few crystal nuclei, and subsequent undercooling produced an unusual fasciculate/spherulitic texture in contrast to the very fine and even grain of the host basalt. A liquid–liquid interface between the flow units shows small-scale lava mixing.
Remote sensing of geological structure in temperate agricultural terrains
Authors: Drury S. A.
Published: May 2009

Agricultural patterns dominate most remotely sensed images of lowland north Europe and camouflage shadow patterns related to topography and hence to underlying geological structure. Images of those parts of the near-infrared spectrum close to absorption features controlled by H–O–H bond stretching in plant cells and soil moisture largely remove this hindrance to interpretation, if they are acquired at an early stage in the growing season. The most easily available and most useful images of this type are those of band 5 from the Landsat Thematic Mapper. Spatial filtering techniques applied to digital images can enhance them for structural interpretation if filter matrices and viewing scales are chosen to match the dimensions of the most common elements of the landscape and the peak of visual acuity. Filters to enhance directional attributes of an agricultural scene give appealing results but contain spurious linear features that masquerade as faults.
Mylonite-dominated footwall geometry in a shear zone, central Pyrenees
Authors: Passchier C. W.
Published: May 2009

A major ductile shear zone in the gneissic core of the Saint-Barthélemy Massif, central Pyrenees, is characterized by an asymmetric shear strain profile defined as mylonite-dominated footwall geometry. The shear zone is part of a low angle fault system in the massif which caused thinning of a sequence of lithologic units and isograds. The shear zone is interpreted as a low angle normal fault zone of probably Cretaceous age, predating Alpine crustal shortening in the central Pyrenees.
The Alpine Fault, New Zealand, near Milford Sound and to the southwest
Authors: Wellman H. W.
Published: May 2009

From 70 km northeast of Milford Sound (44.14° S, 168.55° E) to the coast at Milford Sound (44.53° S, 167.83° E) the trace of the Alpine Fault is nowhere more than 1.2 km from the arc with a centre at 48.81° S, 173.20° E and a radius of 628 km (5.65° latitude). Earthquake epicentres indicate that the arc defines the position of the fault just off Fiordland's outer coast and then to near the north end of Puysegur Trench at 46.9° S, 165.25° E. Along the fault vertically to a depth of 10 km the Fiordland rocks are 0.6 Mg/m3 denser than those to the northwest. Displaced post-glacial topography at and near Milford Sound shows that the dip of the fault is southeast at 75 ± 5° and that the faulting is pure dextral at a rate of at least 46 ± 5 mm/yr.
Petrochemistry of metamorphosed pillows, and the geochemical status of the amphibolites (Proterozoic) from the Sirohi district, Rajasthan, India
Authors: Bhattacharyya P. K. , Mukherjee A. D.
Published: May 2009

Relic pillows in the middle Proterozoic amphibolites, occurring in the Sirohi Road–Abu Road tract of Rajasthan, India exhibit contrasted mineral assemblages from core to rim – mimetic after the crystalline core, the zone of incipient crystallization, and the rim of the original pillows. The major element distribution pattern across the pillows indicates exchange of Na–Al for Ca (Mg, Fe) in an inner reaction zone, surrounding the core and in the inner margin of the rim, and Fe–Al exchange for Ca–Si at the outer margin of the rim.

Despite such exchanges around the rims, these pillows have retained their initial geochemical characteristics internally and thus have largely acted as closed systems during post-emplacement metamorphism. Mineral parageneses indicate that the contrasted mineral assemblages could evolve from domainal characters of the co-existing fluids, the compositions of which were only buffered by the reacting minerals during regional metamorphism.

The major, minor and trace element contents of the pillows and of amphibolites of diverse petrographic character in the region further establish that the pillow interiors and the massive amphibolites were least modified during metamorphism(s), and represent oceanic tholeiites. Their average 2300 ppm K, 4.5 ppm Rb, 150 ppm Sr, along with the K/Rb and K/Sr ratios of 510 and 15 respectively resemble that of the low K-tholeiites, occurring nearest to the trenches in modern island arcs. On the other hand, the higher values of 17300 ppm K, 4.9 ppm Rb, and 210 ppm Sr of the banded and the schistose amphibolites indicate that they were contaminated in various magnitudes by oceanic sediments.
Ferruginous vernadite in an Indian Ocean ferromanganese nodule
Authors: Ostwald J.
Published: May 2009

Select area electron diffraction and microanalysis of the optically dark component of a ferromanganese nodule from the South East Indian Ocean Manganese Field indicate that this is composed of a random stratification of crystallites of vernadite MnO2. (R2O, RO, R2O3)x. yH2O, where R represents elements such as K, Ba, Na, Ca, Mg, and a disordered hydrated iron oxide, possibly ferrihydrite 5Fe2, O3. 9H2O or feroxyhyte δ′-FeOOH. Whether the dark component is an irregular mixed-layer hybrid mineral or a layered accumulation resulting from epitaxy of the above phases is uncertain.
New diminutive camerate crinoids from the Ludlow of Oklahoma
Authors: Frest T. J. , Strimple H. L.
Published: May 2009

Two new camerate crinoids from the Henryhouse (Ludlow) of Oklahoma are evolutionarily convergent on monocyclic inadunates. The prokopicrinid Nanicrinus (new) has a calyx consisting only of three basals (small basal in EA interrary) and five radials. The anal opening is bordered by two radials. Praedicticrinus (new) is a hirneacrinid with anal X as the sole interradial plate participating in the calyx and small basal located in DE interray. Assignment to the Camerata is based largely on presumed phylogenetic relationships. The similar-appearing Permian genera Plesiocrinus, Eutelecrinus, Metaeutelecrinus (new) and Paraeutelecrinus (new) are probable prokopicrinid homeomorphs derived from platycrinitid ancestors. They are assigned to the new family Eutelecrinidae. Adaptation of the definition of homeomorphy utilized by Chauff & Klapper (1978) is advocated for supposed paleontologic cases.
The large-scale structure of the Earth's crust beneath southern Britain
Authors: Whittaker A. , Chadwick R. A.
Published: May 2009

Recently acquired deep seismic reflection profiles recorded to 12 s two-way travel time in southern Britain suggest that the crust beneath this area is commonly divisible, vertically, into three zones.These zones, based upon seismic character, can be related to structural or tectonic units. They comprise an upper zone of cover rocks of various ages, a middle zone of folded and thrust rocks, and a lower zone tentatively identified as metamorphic or crystalline basement. A sketch crustal profile from Dorset to Yorkshire summarizes the data and illustrates the distribution of the zones.
The significance of the proximal end ofCryptograptus tricornis(Carruthers) (Graptolithina)
Authors: Strachan I.
Published: May 2009

Young stages isolated from limestone from Girvan indicate that the first two thecae had unsclerotized walls but apertural rings showing that they opened downwards beside the sicula. The development can thus be matched with that ofGlossograptusand the two families Glossograptidae and Cryptograptidae merged. The recognition of downward-opening thecae inC. tricornisallows the earlier speciesC. schaeferito be more easily accommodated in the genus. Relationships in the family are reviewed.
Isolated pods of subaqueous welded ash-flow tuff: a distal facies of the Capel Curig Volcanic Formation (Ordovician), North Wales
Authors: Howells M. F. , Campbell S. D. G. , Reedman A. J.
Published: May 2009

Acidic welded tuffs of the Capel Curig Volcanic Formation were deposited from ash-flows that transgressed from a proximal subaerial to a distal submarine environment. Isolated pods of welded tuff enveloped by marine sediments represent a distal facies of the formation deposited beyond the limits of the continuous ash-flow tuff sheets. Various mechanisms for the separation of the tuff pods from a parent flow are discussed and it is concluded that it is most likely that the formation of the pods was due to disruption of a subaqueous ash-flow during transport rather than by downslope collapse at the front of a previously deposited ash-flow tuff sheet.
Late Pleistocene deposits and Mollusca from Portland, Dorset
Authors: Keen D. H.
Published: May 2009

The stratigraphy and fauna of terrestrial deposits at Portland Bill is described. The fauna is restricted to the head and is indicative of a cool climate rather than the temperate conditions suggested by earlier authors. An age in the Devensian Glacial Stage is tentatively suggested.
The facing of faults
Authors: Lisle Richard J.
Published: May 2009

It is proposed that the usage of the term structural facing be extended to include fault structures. Fault facing is defined as the direction in a fault plane which is at right angles to the trace of the bedding and is directed towards the younger beds. Certain types of faulted structures are found to have diagnostic patterns of facing variation.
Electron microscope analysis of zoned dolomite rhombs in the Jet Rock Formation (Lower Toarcian) of the Whitby area, U.K.
Authors: Pye K.
Published: May 2009

Zoned dolomite rhombs which occur in the organic-rich Jet Rock Formation (Toarcian) of northeast England have been studied using backscattered scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray microanalysis. The rhombs, which are 5–20 μm in size, are variable in chemical composition, but many consist of a dolomite core surrounded by a zone of ferroan dolomite, ankerite or ferroan calcite. Zoned rhombs occur in early-diagenetic calcite-cemented concretions and layers as well as dispersed throughout the shales. Distributional and textural evidence suggests that they formed mainly by primary precipitation from pore fluids within the zone of bacterial sulphate reduction. The ferroan outer zones probably formed after burial below the sulphate reduction zone when insufficient H2S was available to react with all the Fe2+in solution.
Lithostratigraphy of the Red and Norwich Crags of the Aldeburgh–Orford Area, south-east Suffolk
Authors: Zalasiewicz J. A. , Mathers S. J.
Published: May 2009

Recent investigations indicate that three distinct lithostratigraphical units can be recognized in the Red and Norwich Crag deposits of the area around Aldeburgh and Orford, Suffolk. These effectively represent a refinement of a stratigraphy originally suggested by Prestwich in 1871. A lowermost coarse-grained shelly sand, the Red Crag Formation, rests on an eroded London Clay surface and is banked against the Pliocene Coralline Crag. The Red Crag Formation passes upwards into a fine-grained generally unfossiliferous well-sorted sand, the Chillesford Sand Member, which overlaps the Red Crag Formation to rest directly on the Coralline Crag. The Chillesford Clay Member is regarded as the lateral equivalent of the upper Chillesford Sand Member, the two members together comprising the Norwich Crag Formation in this area. Sections that have been zoned palaeontologically may be integrated into this lithostratigraphical framework. These indicate that the Red Crag Formation correlates with the Pre-Ludhamian Stage, and the Chillesford Sand Member and the Chillesford Clay Member correlate with the Bramertonian Stage. Type sections are established for the three units described.
A Lancefieldian graptolite from the Lake District
Authors: Rushton A. W. A.
Published: May 2009

LargeDictyonemaspecies, includingD. pulchellumT. S. Hall, have been collected from beds in the Uldale Fells (northern Lake District), below strata yieldingDidymograptus protobalticusMonsen. They suggest the presence there of graptolitic beds transitional from Lancefieldian to Bendigonian in age (approximately Tremadoc-Arenig) and suggest that the area may yet provide an internationally correlatable base to the Arenig Series in Britain.
Geochemical evidence for the emplacement of the Whin Sill complex of northern England
Authors: Thorpe R. S. , Macdonald R.
Published: May 2009

The Whin Sill comprises a major quartz tholeiite sill of late Carboniferous age underlying an area of c. 5000 km2 and with a volume of c. 200 km3, associated with contemporaneous dykes emplaced within Carboniferous sedimentary rocks in northeast England. New trace element analyses of chilled margins, sill interiors and dykes indicate that the Whin Sill complex magmas show significant chemical variations in terms of the relatively stable trace elements Th, Ce, Y, Zr, Nb and Ni. These data indicate that the complex was fed by a large number of compositionally distinct magma pulses, and that certain of the dykes may have formed feeder channels for the sill. The chemical characteristics of the sill and dyke samples are consistent with derivation by extensive polybaric fractional crystallization of olivine tholeiite magma derived by partial melting of compositionally heterogeneous mantle peridotite and/or crustal contamination of mantle-derived magmas.
The thrust structures of southern Assynt, Moine thrust zone
Authors: Coward M. P.
Published: May 2009

The Moine thrust zone of southern Assynt forms part of the northwest margin of the Caledonide belt and has aroused controversy concerning amounts and timing of thrust displacement and sequence of thrust development. Recent mapping shows it to have been a foreland propagating thrust sequence; the uppermost ductile Moine thrust formed first, followed by sequences of imbricates, a major thrust (the Ben More thrust) and then several lower duplex zones. This sequence is clear from new observations that many of the earlier thrusts were folded and/or breached during the development of the underlying structures. A displacement of over 54 km has been estimated for the zone as a whole. An alkaline igneous complex, including the large Borrolan syenite, was intruded during the development of the thrust zone and much of it was carried some 30 km to the west-northwest onto the foreland. Late extensional structures in southern Assynt are an integral part of the Caledonide thrust sequence and probably developed from the collapse of the thrust wedge as it climbed from stronger basement rocks on to a weaker cover sequence on the foreland.
The graptolite biostratigraphy of a Llandovery outlier near Llanystumdwy, Gwynedd, North Wales
Authors: Baker S. J.
Published: May 2009

Llandovery strata at Llanystumdwy are described. Ninety graptolite species have been identified enabling the establishment of the following zones:acinaces, cyphus, triangulatus, magnus, leptotheca, convolutus, ?sedgwickii, turriculatusandcrispus.The name Llanystumdwy Mudstone Formation is proposed for previously undescribed mudstones cropping out on the River Dwyfor at Llanystumdwy and includes all strata referable to theacinacestoturriculatuszones. Comparison is made between Llanystumdwy and other areas, notably Northern England and Southern Scotland
The Late Triassic Blue Anchor Formation and the initial Rhaetian marine transgression in south-west Britain
Authors: Mayall M. J.
Published: May 2009

The Blue Anchor Formation of the Upper Trias in south-west Britain is divided into two members. The lower (Rydon Member) was deposited in an evaporitic lacustrine environment whilst the upper (Williton Member) was deposited in a shallow marine environment and represents the initial marine transgression into south-west Britain late in the Triassic Period. Sedimentological and clay mineralogical evidence indicates that the Williton Member is bounded by erosional disconformities and, at present, can only be positively recognised in North Somerset.
Micropalaeontological evidence for land near Cirencester, England, in Forest Marble (Bathonian) times: a preliminary account
Authors: Ware M. , Windle T. M. F.
Published: May 2009

Analysis of a Bathonian ostracod fauna and the microflora from a claypit at Tarlton, Gloucestershire, strongly suggests that land was then nearby. Among the non-marine Ostracoda are cypridacean species similar to lacustrine forms from the French Bathonian. Such an assemblage has not previously been recorded from Britain. The clay is assigned to Bate's revised Bathonian ostracod zone 6, and a palaeogeographical interpretation is offered in terms of recent reconstructions of British Bathonian landmasses.
Columnar sandstone, Island of Bute, Scotland
Authors: Buist D. S.
Published: May 2009

A unique columnar sandstone, produced by the thermal metamorphism of an Upper Old Red quartz arenite, is described, from South Bute, together with other examples of similarly altered sediments from nature and industry. The columnar structure probably developed as a result of the emplacement of a basic dyke via a fissure. In view of the relatively large area exhibiting this structure, metamorphic effects must have been amplified by the agency of steam and volatile constituents of the magma, passing up through the fissure.
Comparative geochemistry of pelites from the Moinian and Appin Group (Dalradian) of Scotland
Authors: Lambert R. St. J. , Winchester J. A. , Holland J. G.
Published: May 2009

Pelitic schists from the Appin Group of the Dalradian Supergroup are all chemically distinct from pelitic schists in the older Moinian Supergroup. In addition, trace-element geochemistry can also discriminate between the individual pelitic schists within the Appin Group, especially those within the Lochaber Subgroup. These differences apparently relate mainly to differences in provenance rather than differences of sedimentary environment, and are sufficiently consistent to offer a means for correlation or identification of pelitic units in areas of the Central Highlands where the stratigraphy is still in dispute.
The Gillbrea Nappe in the Skiddaw Group, Cockermouth, Cumbria, England
Authors: Banham P. H. , Hopper F. M. W. , Jackson J. B.
Published: May 2009

New observations of sedimentary and tectonic structures confirm ‘pre-cleavage’ folding of the Arenig Loweswater Flags and Kirk Stile Slates. A major recumbent fold is thought to have developed by gravity gliding during Arenig-Llanvirnian times.
A trondhjemite vein in the Sulitjelma Gabbro, Norway, and its implications for the age of the Sulitjelma Ophiolite
Authors: Mason Roger
Published: May 2009

The Sulitjelma Gabbro, occurring as a member of the Sulitjelma Ophiolite Complex, and typical of the ophiolite suite in its petrography and geochemistry, is cut by a vein of trondhjemite (plagiogranite). The previous identification of the vein as an offshoot of a continental potassium-rich granite, the Furulund Granite, is wrong. Therefore the Rb-Sr isochron age of 413±34 Ma, obtained from the granite, cannot be taken as the age of intrusion of the Sulitjelma Gabbro.
The use of flexible synthetic rubbers for casts of complex fossils from natural moulds
Authors: Benton M. J. , Walker A. D.
Published: May 2009

Some commercial silicone (Dow Corning Silastic E, J) and PVC (Dugdale DD 118) synthetic rubbers make excellent casting materials for the production of high-fidelity replicas of fossils from complex natural cavities. The methods described avoid tearing of the cast and damage to the mould.
A Coniacian ammonite from the ‘Top Rock’ in the Chalk of Kent
Authors: Gale A. S. , Woodroof P. B.
Published: May 2009

The occurrence of Barroisiceras within the top bed of the Zone of Holaster planus near Dover in Kent provides the first ammonite evidence for the position of the base of the Coniacian in the Chalk of England. Inoceramus cf. rotundatus occurs ½ m above the ‘Top Rock’.
The Ordovician fauna from the Contaya Formation of eastern Peru
Authors: Hughes C. P. , Rickards R. B. , Williams A.
Published: May 2009

The Ordovician Fauna from the Contaya Formation from the lowlands of eastern Peru is fully described for the first time. The fauna is restricted and consists essentially of brachiopods, trilobites and Graptolites and three new species, the brachiopodTissintia simplex, and the trilobitesAnebolithus tafuri and Porterfieldia contayaensisare described. The fauna is shown to have close affinities with those of central Europe and North Africa.
A replacement name for Rhax Lane & Thomas, 1978 (Trilobita) non Hermann, 1804
Authors: Lane P. D. , Thomas A. T.
Published: May 2009

In the Geological Magazine115 (5), 1978, Lane & Thomas proposed the name Rhax for a scutellid of probable late Llandovery from Queensland, Australia.
Interactive processing of satellite images for structural and lithological mapping in northeast Africa
Authors: Berhe S. M. , Rothery D. A.
Published: May 2009

Interactive digital processing of multispectral satellite images (Landsat MSS) using principal components transformations and spatial filtering has clarified the position of continuous sutures linking apparently isolated Pan African (late Proterozoic) ophiolites. These have been field-checked and an arrangement of Pan African suture zones is proposed. Spatial filtering has also highlighted faults with various trends which can be related to the late Precambrian tectonics of the Horn of Africa region.
Facies analysis of the Lo Valdés Formation (Tithonian–Hauterivian) of the High Cordillera of central Chile, and the palaeogeographic evolution of the Andean Basin
Authors: Hallam A. , Biró-Bagóczky L. , Perez E.
Published: May 2009

Facies descriptions and environmental interpretations are given for outstanding sections of marine Tithonian to Hauterivian strata in the High Cordillera of the central Chilean Andes. Comparisons are made with correlative strata in other regions in Chile, and with the Neuquén Basin of west central Argentina. The rich and partly endemic bivalve fauna, which has strong African affinities, shows no change up the stratigrapic sequence that cannot be related to local facies. Water depth is recognized as the main variable controlling the distribution of the bivalve and ammonite faunas. Utilizing data from both Chile and Argentina, a model is put forward for the late Jurassic to mid Cretaceous sequence whereby the facies distributions are accounted for by the interaction of global sea-level changes and regional tectonics in a shallow back-arc basin.
A polymorphic graptolite from concealed Tremadoc rocks of England
Authors: Rushton A. W. A.
Published: May 2009

Abundant specimens from the middle or upper Tremadoc beds in the Napton Fields Borehole, Warwickshire, are referred to one variable species,Kiaerograptus? quasimodosp.nov. Two-stiped forms typical ofKiaerograptusco-exist with ‘one-stiped’ forms in which the first stipe consists only of Th 11. Rare specimens with three primary thecae gave rise to forms with one, two? or three stipes.
The age of the Dinantian (Lower Carboniferous) rocks proved beneath the Kent Coalfield
Authors: Mitchell M.
Published: May 2009

The history of research into the Lower Carboniferous rocks of Kent since Dines' 1933 account of the stratigraphy of the coalfield is outlined. Details of the boreholes that have proved Lower Carboniferous are listed, including notes of the significant fossils that have been identified. The age of the Lower Carboniferous rocks is discussed. Two boreholes yielded faunas of Tournaisian age and i4 proved rocks of Holkerian age. No younger Dinantian strata are known from Kent.
The origin and microstructures of metamorphic felsic dykes emplaced during brittle-ductile extension (southeast Sinai)
Authors: Reymer Arthur P. S.
Published: May 2009

Structural, petrographic and chemical analyses of a set of northeast-trending quartzofeld-spathic dykes in Wadi Kid area (southeastern Sinai) show that they are the product of anatexis of pelitic rocks. Metamorphic P-T data indicate that anatexis could have occurred only 2 km below the present erosion level. The partial melts intruded into overlying rocks during regional metamorphism along a set of northeast-oriented extensional fractures, thereby recrystallizing and in some cases obtaining tectonite fabrics. The fractures were formed perpendicular to the regional mineral lineation and show that the area was within the deeper parts of the brittle–ductile transition zone. The original depth of the presently exposed crustal level corresponds well with the theoretical and experimentally derived depths of the brittle-ductile transition zone in high heat flow regimes. The emplacement of a granitoid pluton or gneiss dome, possibly of dioritic composition, could be responsible for both melting and tensile fracturing of the overlying rocks.
Interactive processing of satellite images for geological interpretation – a case study
Authors: Rothery D. A.
Published: May 2009

Interactive digital processing of satellite images reveals significantly more information than the standard product photographic versions of the same images. Interactively processed images preserve finer details and can show information in areas which appear too dark or too bright on standard product images. This is illustrated by comparisons between both types of image as used in a photogeological interpretation of the tectonics of the Tibetan plateau.
Mid-Cretaceous (Albian-Cenomanian) calcareous nannofossils from Pont du Fahs (northern Tunisia)
Authors: Hojjatzadeh Minoo
Published: May 2009

Calcareous nannofossils from mid-Cretaceous (Albian-Cenomanian) sections at Pont du Fahs (northern Tunisia) allow the recognition of three nannofossil zones-the Prediscosphaera cretacea Zone, the Hayesites albiensis Zone, and the Eiffellithus turriseffeli Zone. A comparative study has been made of the nannofossil assemblages from Pont du Fahs and 14 other sites in North Africa, Western Europe, the North Atlantic and United States.
Evolution of a non-resurgent cauldron: the Late Permian Coombadjha Volcanic Complex, northeastern New South Wales, Australia
Authors: McPhie J.
Published: May 2009

The Coombadjha Volcanic Complex is the remnant of a Late Permian cauldron. It is part of an extensive sequence of silicic calc-alkaline volcanics that covers the southeastern portion of the New England Orogen in NSW. The Complex is elliptical, measuring 15 × 24 km, and is outlined by a ring pluton and an arcuate fault. Bedding in the volcanic units of the Complex defines a structural basin, with steep inward dips at the monoclinal rim and gentle to horizontal orientations near the centre. An older group of outflow ignimbrites, lavas, breccias and volcaniclastic rocks at least 1500 m thick, is conformably overlain by more than 500 m of texturally homogeneous, crystal-rich, dacitic ignimbrite. Ignimbrites of the older group are the products of several discrete eruptions from separate vents, all of which were situated outside the Coombadjha area. Silicic lava domes with volcaniclastic aprons, and a tuff ring, mark the positions of local vents active on a small scale during intervals between the emplacement of the outflow ignimbrites. No significant subsidence occurred, nor did a caldera exist at this stage. Cauldron subsidence occurred in response to the large magnitude eruption that produced the crystal-rich ignimbrite. The central cauldron block was lowered at least 2000 m by downwarping and fault displacement, and remained largely intact. There is no evidence for resurgent doming of the cauldron after subsidence, although igneous activity continued with intrusion of an adamellite ring pluton along much of the cauldron margin. The crystal-rich ignimbrite and the ring pluton are similar in composition and may have been successive products of a common magma source that sustained this simple, single cauldron cycle.
Growth rate observation from the moss-built Checa travertine terrace, central Spain
Authors: Weijermars Ruud , Mulder-Blanken Carla W. , Wiegers Jaap
Published: May 2009

In situ observations of fossil and living specimens of the calcicolous mosses Bryum pseudotriquetrum, Cratoneuron commutatum and Catoscopium nigritum revealed very fast calcite depositional rates. Rhythmic layering in the fossil mosses corresponding with the seasonal climatic cycle suggests that the moss curtain occupied by these three mosses maintains the deposition of spongeous travertine layers at a mean rate of 4 cm a−1. A mean depositional rate of 4.2 cm a−1 may be calculated from measurements of the loss of bicarbonate from the springwater after it percolated through the moss curtain. These rates suggest that the 8 m high travertine terrace of Checa with a surface area of 800 m2 did not exist two millennia ago.

Mosses could be put to man's use for creating natural overgrowths on artificial surfaces, an idea based on an allusion by Wallner. He observed that the thread-forming, blue-green algae Vaucheria builds travertine deposits at an annual rate of 0.7–1.4 cm. We observed that the mosses Cratoneuron commutatum and Bryum pseudotriquetrum may form spongeous travertine layers at respective maximum rates of 11 and 14 cm a−1. This would reduce the time required to build natural overgrowths on artificial objects to a practical period of months.
The early magmatic chronology of Fuerteventura, Canary Islands
Authors: Le Bas M. J. , Rex D. C. , Stillman C. J.
Published: May 2009

Eight new K-Ar determinations are presented which, together with field relations and previous studies, are used to construct a chronology of the volcanic build-up of Fuerteventura. The earliest island-building volcanics are late Cretaceous to early Tertiary alkaline basaltic volcaniclastic sediments, and these may be correlated with the early gabbro/pyroxenite intrusions which were probably subvolcanic to the early edifice. This was followed by a carbonatitic subvolcanic complex then by two later high-level gabbro/pyroxenite plutons, the latter being early Miocene or older. The emplacement of a subsequent middle Miocene gabbro/syenite ring complex caused widespread resetting of the Ar contents of the earlier rocks, but nevertheless consideration of the mineralogy of the rocks in conjunction with the field relations enables the long volcanic history (c. 80 Ma) to be reconstructed.
Possible Late Pleistocene faulting in Iar (West) Connacht, Ireland
Authors: Mohr P.
Published: May 2009

Caledonian and Hercynian faults in Iar Connacht have been examined for evidence of Quaternary movements. Dip–slip displacements are detected, both through preservation of scarps and, in areas of greater denudation, through morphological offsets. The principle sites of this phenomenon are the Maum, Clifden and Gabhla-Shannaveara faults. Tectonic scarps are distinguished from those due to differential erosion and glacial scour. Earthquake risk in Iar Connacht, though slight, is not non-existent.
Wall-rock silicification associated with fluorite veins in Carboniferous limestone at Butts Quarry, Derbyshire, England
Authors: Kanaris-Sotiriou R. , Neves R. , Gibb F. G. F.
Published: May 2009

Wall rocks on either side of narrow fluorite veins cutting Dinantian Limestones at Butts Quarry, Derbyshire, exhibit unusual and spectacular alteration structures. Buff, ‘blackened’ and grey limestone lithologies, containing significant amounts of euhedral quartz crystals, occur in a zoned sequence adjacent to the veins. The alteration structures are attributed to a two-stage process involving silicification and subsequent re-mobilization of silica by fluids passing along the vein.
Introduction
Authors: Brown G. Malcolm
Published: May 2009

The Tertiary volcanic centre that dominates the constitution of Rhum, one of the Scottish Inner Hebridean group of islands, is immediately provocative to the visiting geologist. The higher mountains are entirely ultrabasic in composition and their near-horizontal, terraced layers remain nearly constant in composition to about 1 km above sea level. Any initial assumption of geological simplicity is quickly dispelled by those and more detailed features. Horizontal layers of ultrabasic rocks with coarsely crystalline texture do not fit happily on a Tertiary landscape, towering high above the adjacent Hebridean lava flows of similar age. And what of the rocks themselves? Thin layers entirely of calcic plagioclase feldspar compete for attention with thick olivine-rich layers, while any day of traversing the Hallival or Askival mountain slopes will reveal a wealth of superbly exposed question marks in the form of spinel–sulphide layers, slump structures, finger structures, ‘harrisitic olivine’ formations, undulatory ‘trough-like’ structures, ultrabasic veins and currently lesser features. Search as one may (and little is hidden from view), there is no marginal gabbroic envelope between the ultrabasics and the country rocks that would lead to a Skaergaard analogy, and no overlying gabbroic layered rocks that would elicit guidelines from the Bushveld or Stillwater intrusions. This is Rhum, and much of what is on that small island is unique and, indeed, still defies full explanation. It is the achievement of this issue, through its several contributors whose voices succeed mine, that the uniqueness of Rhum is welcomed, many of the problems challenged, and many of the secrets unravelled.
The Tertiary lavas and sediments of northwest Rhum, Inner Hebrides
Authors: Emeleus C. H.
Published: May 2009

Several small outliers of Tertiary lavas and sediments rest with strong unconformity on a buried landscape eroded from Torridonian sediments and Tertiary granophyre. Erosion continued during the period of sediment and lava accumulation. Four formations are recognized; these are, in order of increasing age, the Orval Formation (hawaiite and basaltic hawaiite lavas), the Guirdil Formation (icelandite lavas, interbedded conglomerates), the Upper Fionchra Formation (tholeiitic basaltic andesite lavas, hyaloclastite deposits, basal conglomerate) and the Lower Fionchra Formation (alkali and transitional basalt, basaltic hawaiite and hawaiite lava flows, basal conglomerate); each is separated by an erosional interval. Clasts in the conglomerates reveal a history of erosion of a terrain exposing gneisses, Torridonian sediments, igneous rocks derived from the Rhum Tertiary Central Complex (including allivalites), and Tertiary lavas of local origin but also including, in the oldest conglomerates, tholeiitic basalts not now preserved on or near Rhum. Prior to and during lava and sediment accumulation, erosion on Rhum had cut down to a level similar to that of the present day, although not to the extent that high-grade thermally altered rocks, which are a marked feature of the Central Complex, were being eroded in any quantity. A sequence of east–west trending valleys, possibly initiated on the line of the earlier Main Ring Fault, drained the area of the Central Complex which then, as now, must have been high ground. Small lakes occasionally formed in the valleys allowing the accumulation of fine-grained sediment with plant remains, and promoting the formation of hyaloclastite deposits when buried by later flows. No source for any of the lava formations is preserved on Rhum; they are thought to have come from feeders north of Rhum, possibly near Canna, and to have ponded against the hills and valleys near and in the Central Complex.

The oldest tholeiitic lavas, not now found in situ, were followed by alkali and transitional flows compositionally similar to the Skye Main Lava Series but characteristically feldsparphyric; the most mafic also contain phenocrysts of magnesian olivine (with included Cr-Al-rich spinels) and aluminous spinel. Both the early alkalic/transitional basalts and the youngest hawaiites and basaltic hawaiites equilibrated at pressures < 9 kb; the tholeiitic basaltic andesites and icelandites equilibrated at relatively shallows depths.

Apart from a few N–S to NW–SE-trending basalt dykes, the lava formations represent the youngest Tertiary igneous event on Rhum.
Pyroclastic rocks in the Cnapan Breaca felsite, Rhum
Authors: Williams P. J.
Published: May 2009

The Cnapan Breaca felsite sheet contains strongly devitrified pyroclastic rocks including welded tuffs. These indicate formation in a high level, surficial or sub-volcanic environment. The gross structure and lithological associations of the sheet are similar to those of some ignimbrites. These observations support a resurgent caldera model for the evolution of the Rhum centre and raise some doubts about previous interpretations of the felsite-breccia association on the island.
The early igneous and tectonic history of the Rhum Tertiary Volcanic Centre
Authors: Emeleus C. H. , Wadsworth W. J. , Smith N. J.
Published: May 2009

Early Tertiary igneous activity on Rhum was preceded by doming and the formation of a major arcuate fault system, the Main Ring Fault (MRF), within which Lewisian gneisses, Torridonian sediments and younger rocks were uplifted by as much as 2 km. Doming and uplift are attributed to the diapiric rise of acid magma which ultimately formed the granophyres and felsites of Rhum. Felsite emplacement was accompanied and immediately preceded by the formation of explosion breccias and tuffisites. This phase involves massive gas escape along the MRF fractures; it marked a period of major subsidence within the MRF during which fossiliferous Jurassic sediments and relics of Tertiary lava flows were brought to low structural levels within the MRF. Finally, a further period of uplift, again of about 2 km, took place once more bringing gneisses and basal Torridonian sediments within the MRF to high structural levels. The driving force for this last phase of uplift may have been provided by a further uprise of acid magma or, more realistically, may have been directly connected with emplacement of layered ultrabasic rocks which now form the core of the Rhum centre.