bluuebunny/crossref_metadata_2025_split huggingface dataset:
Growth rate observation from the moss-built Checa travertine terrace, central Spain
Authors: Weijermars Ruud , Mulder-Blanken Carla W. , Wiegers Jaap 
Published: May 2009

AbstractIn 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

AbstractEight 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

AbstractCaledonian 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

AbstractWall 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.
The Tertiary lavas and sediments of northwest Rhum, Inner Hebrides
Authors: Emeleus C. H. 
Published: May 2009

AbstractSeveral 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

AbstractThe 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

AbstractEarly 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.
Cambro-Ordovician strata in Ny Friesland, Spitsbergen and their palaeotectonic significance
Authors: Swett K. 
Published: May 2009

SummaryField and petrologic investigations of Cambro-Ordovician strata in Ny Friesland, Spitsbergen reveal a stratigraphic, sedimentologic, and diagenetic history for those rocks that bear striking similarities to coeval strata in central East Greenland, northwest Scotland and western Newfoundland. Parallels between these presently widely separated areas include: stratigraphic sequence (including enigmatic gaps), sedimentary structures, faunal assemblages, trace fossils, geochemical anomalies, and diagenetic sequences. It seems inescapable that the Cambro-Ordovician successions in Ny Friesland, central East Greenland, northwest Scotland, and western Newfoundland were developed on a once contiguous shelf on the margin of the lapetus Ocean. A tentative sequential tectono-sedimentological facies model of the ‘North Atlantic Geosyncline’ extending in time from late Proterozoic to the opening of the Atlantic Ocean is proposed to explain the empirical data. Slow closure of the lapetus basin, simultaneously involving transgression of the ‘North American’ plate and subduction of lapetus oceanic crust beneath a Euro-Balto-Scandinavian plate, followed by collision of the two continental plates, in turn followed by reopening along the approximate collision boundary appears to explain the observed relationships. This palaeotectonic/sedimentologic model is subject to further testing. The lithostratigraphic scheme is further refined.
‘Basalt fingers’ – origin of columnar joints?
Authors: Kantha L. H. 
Published: May 2009

SummaryThermal stresses due to contraction during cooling have been widely accepted as the origin of columnar structures in certain igneous rocks. It is proposed that these highly ordered structures could be the result of a double-diffusive convective process in the melt during cooling, a process analogous to salt fingers observed in the laboratory and the oceans. Salt fingers are driven by appropriate differences in heat and salt content at the top and bottom of a stably stratified water column. In molten basalts, temperature and chemical-compositional differences between the top and bottom of a stagnant melt could drive highly regular columnar ‘finger’ motions in the melt. When solidification takes place eventually, cracks due to contraction during cooling would then have preferred paths of propagation into the interior from the surface along the junctions of adjacent ‘basalt fingers’ giving rise to columnar jointing. Morphological evidence supporting the finger hypothesis is cited and useful ways of gathering further field data that would shed some light on the validity of the hypothesis are suggested. For the benefit of geologists not familiar with double-diffusive processes, an up-to-date review of these flow phenomena is included.
Gas pipes in Eocambrian volcanic breccias
Authors: Duyverman H. J. , Roobol M. J. 
Published: May 2009

SummaryEocambrian volcanic breccias of angular dacite and andesite clasts at Wadi Fatima, Kingdom of Saudi Arabia, contain perfectly preserved gas pipe structures. Only the latter identify them as lithic-rich, pyroclastic flow breccias of Pelean type. Without the gas pipes it would not be possible to identify them as pyroclastic and different from epiclastic breccias originating as mudflows, lahars or avalanches. The pyroclastic flow breccias constitute a minor component of the volcanic Fatima Group dominated by pumiceous water deposited sediments and subaerial welded tuffs.
Fluvio-lacustrine cyclothems from the Oligocene of Hampshire
Authors: Daley B. 
Published: May 2009

SummaryEach fluvio-lacustrine cyclothem may include the following lithotypes (in ascending order): (a) irregularly laminated silts and muds; (b) regularly laminated muds and silts; (c) muds with or without molluscan partings and bands; (d) colour mottled muds. Each cycle reflects a change from flowing water conditions (fluvial) to non-flowing water conditions (lacustrine), culminating in some cases with the formation of marsh. Each lithotype is thought to represent the environmental changes which resulted from the silting up of inter-channel depressions on a flood plain. Successive cyclothems possibly reflect renewed flooding following an increase in river level during more pluvial periods.
Significance of pebble and mineral lineation in the Chamba syncline of Punjab Himalaya, Himachal Pradesh, India
Authors: Thakur V. C. , Tandon S. K. 
Published: May 2009

SummaryA pebble lineation has been produced as a result of the first phase deformation that formed the Chamba syncline and the associated slaty cleavage. The lineation indicates the principal direction of maximum elongation of the finite tectonic strain ellipsoid of the first phase deformation and lies nearly normal to the axial direction of the Chamba syncline. The mineral lineation and the long axes of deformed crinoid ossicles show paralelism to subparallelism with the pebble lineation. The second and third phases of deformation, which are characterized by open style folds and associated crenulation cleavage, appear to be of weak magnitude and have not modified the orientations of pebble lineation.
An unusual occurrence of quartz and amorphous silica at Carmean, Moneymore, Co. Antrim
Authors: Preston J. 
Published: May 2009

SummaryCavities in Cretaceous chalk, Co. Antrim, contain spongy silica. SEM photographs show minute doubly terminated quartz crystals trapped in fibrous mats of amorphous silica. The absence of both opal diffraction lines and a globular structure indicate the prior existence of gelatinous silica which prevented settling of the suspended quartz crystals. Drying and shrinkage of the gel produced the spongy deposit.
The occurrence of the Ordovician brachiopod Heterorthis alternata (J. de C. Sowerby) in the topmost Onnian of the type Caradoc area
Authors: Harper D. A. T. 
Published: May 2009

SummaryThe orthidine brachiopod Heterorthis alternata (J. de C. Sowerby 1839) is here recorded from the River Onny Cliff Section at an horizon high in the Onnia superba Zone of the Onnian Stage. Previously it had only been recorded from rocks of Upper Longvillian, Marshbrookian and Actonian age of South Salop and of Upper Caradoc age of Morocco.
Age, palaeomagnetism and chemistry of melilite basalts in the Southern Cape, South Africa
Authors: Duncan R. A. , Hargraves R. B. , Brey G. P. 
Published: May 2009

SummaryPost-Karroo melilite basalts intrude Cretaceous and older sedimentary units in the Cape Province, South Africa. K-Ar ages determined from 4 occurrences range from 63–75 Ma b.p. (Late Cretaceous to earliest Tertiary) and are significantly older than alkaline intrusions to the 5, on the Alphard Bank. These igneous intrusions may be part of a linear trend that connects young oceanic volcanism at Bouvet Island with Cretaceous kimberlitic activity in southern Africa. This lineament nearly parallels the Walvis Ridge and a hot spot model for its origin is examined.
Ephemeral sedimentary structures formed during Aeolian deflation of beaches
Authors: Carter R. W. G. 
Published: May 2009

SummaryStructures formed during wind deflation of poorly sorted beach sediments have rarely been described in the literature. However, a number of distinct forms exist including capped pedestals, asymmetrical ‘tear’ structures and scoured or impacted crusts. All these phenomena result from differential spatial erosion of the beach surface by wind, caused by textural or compositional variations. Ephemeral structures are indicative of rapidly changing geomorphological conditions and their presence may also exert control over continuing aeolian processes.
Strain and shape analysis from the deformed pyrites with a note on their preferred orientation
Authors: Sen R. , Mukherjee A. D. 
Published: May 2009

SummaryFrom the distribution and orientation of final axial ratios of deformed elliptical pyrites and boudins, initial distributions are determined. A strain ellipse is then reconstructed using the shape factor grid. The long axis of the strain ellipsoid represents the trend of regional fold axis (the fold is of flexural slip type). The dimensional orientation (elongation) of the pyrites and the boudins is referred to the homogeneous strain components in the fold. Petrofabrics of the pyrite cubes indicate that they have a preferred orientation.
Chemical petrology and K–Ar ages of the Lewisian gneisses of Rona, near Skye, Scotland
Authors: Holland J. G. , Lambert R. ST J. 
Published: May 2009

SummaryThe average chemical composition of the biotite–gneisses of Rona is very close to that of similar gneisses in the Laxford area, and nearly as close to those of the Torridon area. The biotite–gneisses of Rona are slightly richer in Li, Ba and Zr, slightly lower in Mg and Sr and have a higher Fe2O3/MgO ratio than their mainland counterparts. Biotite mineral ages of 1400 m.y. and hornblende mineral ages of up to 1750 m.y. indicate a similar late-metamorphic history to that of the mainland Laxford assemblage.
Revision of the stratigraphic position of cynodonts from the upper part of the Karroo (Gondwana) System in Lesotho
Authors: Turner B. R. 
Published: May 2009

SummaryCynodonts from two localities in Lesotho have been assigned by earlier workers to the Triassic Molteno beds of the upper part of the Karroo (Gondwana) System. These are important inasmuch as they were thought to represent the only evidence of reptilian remains in an otherwise barren sequence and may help to bridge the palaeontological gap in this part of the Karroo succession. Critical examination of both localities during the course of a regional analysis of the Molteno basin showed discrepancies in stratigraphic interpretation. These discrepancies are pointed out and the stratigraphy revised as a result of which the cynodonts can no longer be assigned to the Molteno beds; one is in the underlyingCynognathuszone (confirmed by further finds of typicalCynognathuszone reptiles) and the other is in the Red beds above. At the Tsoaning River locality a pebble conglomerate resting on an eroded surface provides a good local marker for the base of the Molteno. The implications of this with respect to the fossil flora and fauna at these localities are briefly discussed.
Quantitative petrography of mafic dikes from the central Bighorn Mountains, Wyoming
Authors: Heimlich R. A. , Gallagher G. L. , Shotwell L. B. 
Published: May 2009

SummaryTwo groups of mafic dikes occur within a terrain of metasomatic granitic rocks and quartzofeldspathic gneiss in the central Bighorn Mountains of Wyoming. The younger group consists of dolerite dikes which possess ophitic, subophitic, hypidio morphic-granular and microporphyritic textures. Mineralogically, the dolerites consist primarily of plagioclase (average An 54), augite (average Ca: Mg: Fe = 41: 43: 16) and uralite. The older dikes are metadolerites which possess granoblastic margins that grade into interiors characterized by relict subophitic and locally, porphyriti texture. Dike margins consist of fresh plagioclase and hornblende primarily. Interiors are principally clouded plagioclase (average An 46), augite (average Ca: Mg: Fe = 39: 54: 7) and uralite and/or hornblende. Textural, mineralogic and chemical data indicate that the meta-dolerites were derived from an earlier generation of mafic dikes comparable to the unmeta-morphosed dolerites in the area. The dikes were metamorphosed under low amphibolite facies conditions during the last regional metamorphic event which affected the country rock. During their metamorphism, minimal amounts of water from the country rock facilitated the total recrystallization of the metadolerite margins and the complete or nearly complete replacement of pyroxene by hornblende in the margins. In general, dike interiors underwent no textural changes other than partial destruction of the original subophitic plagioclase–pyroxene relationship as the pyroxene was replaced peripherally by hornblende. This process was accompanied by diffusion of calcium from the plagioclase to form the hornblende, and by diffusion of iron from the augite to cause the clouding of adjacent plagioclase.
Virgellar meshworks and sicular spinosity in Llandovery graptoloids
Authors: Rickards R. B. , Koren' T. N. 
Published: May 2009

SummaryOrthograptus obuti sp.nov. and Orthograptus insectiformis Nicholson are shown to exhibit a complex proximal meshwork developed from a much-divided virgella which closely resembles retiolitid clathrial and lacinial networks. The virgellar meshworks tend to enclose the rhabdosome, at least for the first few thecal pairs, and may support a tenuous periderm. This kind of virgellar complexity is contrasted with a newly discovered form of sicular spinosity represented by the species Glyptograptus (Pseudoglyptograptus) tabukensis sp.nov. and G. (P.) rhayaderensis sp.nov
Mechanical production of metamorphic banding—a critical appraisal
Authors: Shelley D. 
Published: May 2009

SummaryThe mechanical process for producing foliation (banding) in metamorphic rocks, as proposed by Schmidt (1932), is shown to be inadequate. Examples in the literature ascribed to the mechanism are insufficiently supported and the metallurgical analogy for the process is found to be false. A possible restatement of a mechanical process by analogy with particle interaction effects during the laminar flow of suspensions is discussed. Evidence from metamorphic rocks indicates, however, that the modified mechanical process cannot be responsible for common metamorphic layering.
Descriptive microstructural terminology for high-grade metamorphic tectonites
Authors: Collerson K. D. 
Published: May 2009

SummaryIn high-grade regionally metamorphosed tectonites three varieties of micro- structures are recognized, namely (1) granoblastic, (2) granoblastic elongate, (3) anastomosing. Relative and absolute grain size, combined with grain boundary shape, provide the basis for their description. This microstructural classification is directly applicable to granulite facies and transitional granulite to amphibolite facies rocks and avoids some of the shortcomings inherent in previous terminologies.
The Ordovician Graptolite GenusParaglossograptusMu
Authors: Rickards R. B. 
Published: May 2009

SummaryThe lacinia inParaglossograptusMu is shown to consist of four ladder-like networks which are independent of each other and have no direct connection with spinose thecal apertural processes. The lacinial networks are positioned at the corners of the quadrangular rhabdosome as inParaglossograptus? sp. of Whittington & Rickards, which is described here asParaglossograptus proteus(Harris & Thomas).Paraglossograptus etheridgei(Harris, 1924), the important Ordovician zone fossil, together withP. typicalisMu andP. latusHsü, are considered junior synonyms ofReteograptus tentaculatusJ. Hall, 1865.P. tentaculatus(J. Hall, 1865), is regarded here as the type species ofParaglossograptusMu. Detailed comparisons are made betweenP. tentaculatusand the stratigraphically youngerP. proteus(Harris & Thomas), and withGlossograptus holmiBulman, a species in some ways intermediate betweenParaglossograptusandGlossograptusEmmons.
Turbidite origin of some laminated mudstones
Authors: Piper David J. W. 
Published: May 2009

SummaryMany deep water marine muds, including lower Palaeozoic mudstones from Britain, have thin graded beds in which mud and silt laminae alternate, with the silt becoming finer and less abundant upwards. Of the known deep-sea depositional processes, turbidity currents are the most likely cause of such graded laminated beds. The lamination may be produced by alternating cohesive and granular bed conditions. Much more careful examination of laminated fine grained terrigenous sediment is needed.