bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rootless vents in welded ash-flow tuffs from northern Snowdonia, North Wales, indicating deposition in a shallow water environment
Authors: Wright J. V. , Coward M. P. 
Published: May 2009

SummaryIn northern Snowdonia welded ash-flow tuffs, correlated with the Pitt's Head Tuff Formation occur intercalated with Caradoc shallow marine shelf sediments. Within the tuffs there are vent-like structures which have a diapiric form where fiamme are drawn in towards a central core. The cores may have a constrictional linear fabric of streaked out fiamme, or may consist of vitrous tuff surrounded by a zone of buckled planar fiamme. There are associated zones of quartz nodules which are thought to represent quartz filled vesicles. The diapiric structures are believed to be rootless vents. Steam generated by the heat of the flow in contact with shallow water is thought to have caused explosive disruption of the tuffs as consolidation and welding occurred. These structures are thus themselves indicators of deposition of ash-flow tuffs in a shallow water environment.
Comparative petrography of deformed and undeformed migmatites from the Grampian Highlands of Scotland
Authors: Ashworth J. R. 
Published: May 2009

SummaryFabrics in migmatites from Portsoy in the NE Dalradian are compared with those in paratectonic and pretectonic migmatites from deeper structural levels of the Northern Grampain Caledonides. Paratectonic leucosomes, from Portsoy and Mid-Strathspey, have weak biotite fabrics. They lack the biotite foliation which is strongly developed in pretectonic leucosomes from the Upper Findhorn area. In conjunction with the sequence of deformation, intrusion and metamorphism in Banffshire, the fabric data indicate that migmatization at Portsoy was paratectonic with respect to the local F, folding. Partial melts generated in the aureole of the pre-F3 basic intrusions were, in some rocks, still mobile during F3 and completely crystalline only after the formation of small F3 folds. Granitic leucosomes in Mid-Strathspey were formed within the time-span of a deformation episode. Petrographic measurements show that these leucosomes have approximately minimum-melting compositions in Qz-Ab-An-Or, despite some deformation and retrograde alteration. They are comparable with the Portsoy migmatites in grain size and in complexity of leucosome shapes, and they are tentatively interpreted as products of incipient partial melting without dehydration of biotite.
Mixed benmoreite/trachyte flows from Kenya and their bearing on the Daly Gap
Authors: Jones W. B. 
Published: May 2009

SummaryBlebs of anorthoclase-phyric purple rock, usually up to 10 cm but occasionally up to 30 cm in diameter, occur in trachyte lavas of the volcanoes Kilombe and Kapkut, Kenya. The blebs have bulbous outlines and chilled margins and are therefore considered to have been liquid when incorporated in the trachyte. Chemically similar to the benmoreites of Hawaii, Skye and the southern Kenya Rift Valley, they bridge a gap in an otherwise complete sequence of lavas from basalt to trachyte. The failure of benmoreite to erupt as a lava is attributed to viscosity reaching a maximum among intermediate lavas.
The occurrence of Mesozoic oceanic floor and ancient continental crust on South Georgia
Authors: Storey B. C. , Mair B. F. , Bell C. M. 
Published: May 2009

SummaryThe Larsen Harbour Formation of southern South Georgia is part of an ophiolite sequence of submarine lavas and sheeted dykes emplaced into metasedimentary country rocks. The metasediments are remnants of a pre-Cretaceous continental crust which had been subject to regional metamorphism and polyphase deformation prior to intrusion by a variety of acid and basic igneous rocks (roots of the ophiolitic sequence). It is proposed that the segment of continental crust and the Larsen Harbour Formation formed the floor of a back-arc basin which was infilled during Early Cretaceous time by a thick sequence of volcaniclastic sediments (Cumberland Bay Formation).
The sillimanite zones of the Huntly-Portsoy area in the north-east Dalradian, Scotland
Authors: Ashworth J. R. 
Published: May 2009

SummaryThe distribution of andalusite, kyanite and sillimanite in an important part of the NE Dalradian is mapped. Sillimanite represents a late episode overprinted on the regional Andalusite and Kyanite Zones. The spatial distribution of sillimanite confirms that the heat source for the sillimanite-grade metamorphism in this area was the Newer (or Younger) Basic magma. The sillimanitic aureole of the Newer Basic intrusives is divisible into a Sillimanite Zone and a higher-grade Sillimanite—potash feldspar Zone. Relict andalusite is common in the Sillimanite Zone. Coarse muscovite replacing other minerals is primary in both zones, and should not be confused with late retrograde effects. Electron-probe analytical data on the Sillimanite–potash feldspar zone paragenesis of muscovite are presented. In this, its type area, the so-called ‘Boyne Line’ does not exist; the concept of such a tectonic dislocation arose through misinterpretation of the metamorphic effects.
A postulated post-Hercynian rift valley system in southern Britain
Authors: Whittaker A. 
Published: May 2009

SummaryIt is suggested that post-(Hercynian)orogenic tensional forces may have initiated a major rift valley system in the Palaeozoic rocks of southern Britain. Large graben structures may underlie the Bristol Channel, the Severn Basin and the Weald Jurassic trough. Smaller graben structures are present in Devon and are associated with extrusive, potassium-rich lavas. The bounding faults of the larger postulated grabens may have been active during early Mesozoic times and may have fundamentally controlled sedimentation in local sags. A model is proposed which ascribes the development of fault-bounded Permo-Triassic basins and Jurassic axes of uplift to fracturing in the Palaeozoic basement.
Late Precambrian glacial climate and the Earth's obliquity
Authors: Williams G. E. 
Published: May 2009

SummaryLate Precambrian (∼ 750±200 Ma) glaciogenic sequences exhibit substantial evidence for marked climatic inequability of seasonal and longer periodicity (10° to ∼ 106yrs): (1) tillites are closely associated with dolomites, limestones and evaporites apparently of warm-water origin; (2) tillites occur with red beds and iron-formations whose iron probably was derived ultimately from lateritic weathering; (3) glacial dropstones occur locally within carbonates and iron-formations; (4) laminae, interpreted asvarvesby many workers, are common in argillites, carbonates and iron-formations; and (5) permafrost structures attributable to repeated seasonal changes of temperature are locally abundant. Such climatic, particularlyseasonalinequability apparently conflicts however with the probable low (≲30°) palaeolatitudes of deposition of numerous late Precambrian glaciogenic sequences.The contradictions presented by such sequences may be resolved by postulating a considerably increased obliquity of the ecliptic (ε) in late Precambrian time. Substantial increase in e would: (1) greatly amplify global seasonality; (2) weaken climatic zonation, thus allowing warm-water sedimentation and lateritic weathering over wide latitudes; and (3) increase the ratio of radiation received annually at either pole to that received at the equator, so when 54° < ε < 126° low and middle latitudes (≤ 43°) would be glaciated in preference to the poles. Ice sheets and permafrost thus can be envisaged principally in low and middle latitudes with contiguous warm-water and iron-rich facies under a markedly seasonal climate. The concept of secular change of e is supported by other geological evidence.
The crystallization of the teschenite from the Lugar Sill, Ayrshire
Authors: Phillips W. J. 
Published: May 2009

SUMMARYTwelve stages in the crystallization of the teschenite are defined by the commencement or cessation of crystallization of particular minerals. Ocellar structures, outlined by tangentially arranged biotite flakes, developed in liquid pockets after the sill had begun to consolidate, due to the coalescence of crystalline masses. It is thought that these ocellar structures were formed by the growth of gas bubbles and that this caused the expansion and fracturing of the partially consolidated sill. It is argued that the separation of the gas phase was the result of a retrograde increase in the vapour pressure during crystallization.
Sedimentary and igneous trends on AFM diagrams
Authors: Robinson D. , Leake B. E. 
Published: May 2009

SummaryIt is pointed out that some chemically analysed sedimentary rock series when plotted on AFM diagrams (A = Na2O + K2O; F = total iron as FeO; M = MgO) partly mimic trends generally considered characteristic of igneous variation, especially the calc-alkali trend. Although the scatter in sedimentary rock plots is generally greater than that given by igneous rocks this is not necessarily so for calc-alkali suites often show considerable scatter. These observations should be considered when deducing the origin of highly metamorphosed gneisses and quartzo-feldspathic rocks that might be meta-arkoses, meta-granites or meta-volcanic rocks.
Petrochemistry of Paleozoic spilites of the eastern Alps (Austria)
Authors: Loeschke J. 
Published: May 2009

SummaryIn the Karawanken Mountains (SE Austria) spilites (pillow lavas and sills) are found intercalated in a sequence of Paleozoic slates and graywackes. The petrogenesis of these spilites is interpreted as follows: The pillow lavas and sills consolidated as mugearites and hawaiites, which were derived from an alkali olivine-basaltic magma by fractional crystallization. Under low temperature metamorphic conditions water entered into the rocks predominantly from external sources. The primary minerals (Na-Ca plagioclase, pyroxene and glass) were thus replaced either partially or completely by minerals characteristic of spilites (albite, chlorite, epidote and others). The spilites analysed are of secondary origin. They are compared with spilites and basalts of other (continental and oceanic) areas.
Evidence of Precambrian block-faulting in the western margin of the Afar depression, Ethiopia
Authors: Kazmin V. , Garland C. R. 
Published: May 2009

SummaryRegional mapping in the eastern escarpment of the Ethiopian plateau indicated Precambrian block-faulted structures which have been felt in sedimentation and tectonics for more than 1000 m. y. and which controlled to some extent the opening of the Afar.
Some conventional potassium–argon and 40Ar/39Ar age studies of glauconite
Authors: Brereton N. R. , Hooker P. J. , Miller J. A. 
Published: May 2009

Summary40Ar/39Ar age studies of some glauconites from well-known stratigraphical horizons reveal unexpectedly high ages compared with the conventional K–Ar age determinations. These have been interpreted in terms of nuclear and physico-chemical reactions sustained by the glauconites in the reactor. These impose severe limitations on the use of glauconite in the 40Ar/39Ar irradiation technique.
Coignouina decora sp. nov. and Carbonocoryphe hahnorum sp. nov. (Trilobita) from a Viséan fissure deposit near Clitheroe, Lancs
Authors: Miller J. 
Published: May 2009

SummaryThe fauna of a Lower Carboniferous (S1) fissure near Clitheroe, Lancashire, is listed. Coignouina acanthina sp. nov. (Otarionidae) is described, together with its unusual ‘eye-mound’ which bears tubercles rather than lenses. Note is made of new material of C. acanthina (Coignou) which necessitates modification of Osmólska's (1967) reconstruction of the cephalon. Carbonocoryphe hahnorum sp. nov. (Proetidae) is also described and a brief account presented of its variation, postlarval ontogeny and palaeo-ecology.
The Metamorphism of the Manx Slate Series, Isle of Man
Authors: Simpson Alexander 
Published: May 2009

AbstractPrevious research by the present author has established the Caledonian tectonic history of the Manx Slate Series. In particular three episodes of folding (F1, F2, F3) were recognized. The present contribution describes the sequence of metamorphic textures impressed on these metasediments during this polyphase deformation.Two distinct episodes of metamorphism have affected the Manx Slate Series. A syn-tectonic F1 metamorphism produced a chloritezone alteration throughout the Island. A later F2 metamorphism was primarily responsible for the growth of small porphyroblasts of several minerals within the pre-existing F1 fabric. This second metamorphism is confined to the hinge of the large-scale F2 Manx synform and its effects are visible in an elongate belt following the middle of the Island. The emplacement of the porphyroblasts began during the F2 movement and continued into the static interval which preceded the third (F3) movement-phase. It was completed prior to the F3 deformation.
A Study of Possible Factors concerning Garnet Formation in Rocks from Ardara, Co. Donegal, Ireland
Authors: Jones K. A. , Galwey A. K. 
Published: May 2009

AbstractChemical and modal analyses have been made for a series of ten homogeneous specimens of meta-sediments, with identical metamorphic histories, from the aureôle of the Ardara pluton. Results showed that total amount of garnet was determined by the quanity of “free ferrous oxide” (assuming that the reaction: FeO + Fe2O3→ Fe3O4, has gone to completion) in the rock. Size distribution curves showed that each specimen contained crystals with a preferred radius and throughout the series a quantitative relation between the preferred radius and the frequency distribution about this value was observed.Measurement of the number of crystals per unit volume showed that this gave trends with functions of the chemical composition of the rock. A discussion of the mechanism of garnet formation in terms of chemical laws of nucleation and growth is given.
The Pre-Cambrian and Lower Palaeozoic Rocks of South-east Co. Wexford, Eire
Authors: Crimes T. P. , Dhonau N. B. 
Published: May 2009

AbstractThe pre-Carboniferous rocks exposed along the coast of Co. Wexford from Rosslare to Bannow Island have been re-examined. Four distinct units are recognized: the Rosslare Complex, the Cul-lenstown Group, the Tagoat Group and the Bannow Group.The Rosslare Complex and the Cullenstown Group are suggested to be of Pre-Cambrian age. A correlation is proposed between the Cullenstown Group and part of the Mona Complex of Anglesey; the Rosslare Complex is thought to be much older. It is suggested tentatively that all the Bannow Group may be of Ordovician age.
The Polarisbreen Series and other evidences of late Pre-Cambrian Ice Ages in Spitsbergen
Authors: Wilson C. B. , Harland W. B. 
Published: May 2009

AbstractDetails of the Infra-Cambrian Polarisbreen Series are given, arising partly out of observations made since they were defined in outline by the authors in 1956. The Polarisbreen Series includes the distinctive Polarisbreen Tillite Formation, which correlated with the neighbouring Sveanor Formation of Nordaustlandet and with other tillites in Vestspitsbergen. They are regarded as a product of the great infra-Cambrian ice age and are correlated with world-wide tillite horizons of this age.
On the Association of an Indurated Basic Tuff and a Felsite Intrusion in the Kilchrist Vent, Skye.
Authors: Ray Prem S. 
Published: May 2009

AbstractA metamorphosed basic tuff and a felsite and a felsite intrusion are described. Presence of laminar structure in the matrix of the tuff and of veinlets of tuff penetrating and acid xenolith enclosed in the tuff indicates that the fragmental assemblage moved in a manner similar in final effect to fluid injection. A felsite-tuff which grades into the felsite is thought to be the remnant of the emplaced material subsequently metasomatized in situ to produce the felsite.
Brood Pouches in the Devonian Brachiopod Uncites
Authors: Rudwick M. J. S. 
Published: May 2009

AbstractSome, but not all, specimens of Uncites have a pair of pouches formed by invagination of the shell margin. These are interpreted as brood pouches. They are compared with the brood pouches of Lacazella and other living brachiopods, and of the living bivalves Thecalia and Milneria.
A Note on the Pleistocene Deposit at Grantchester, Cambridgeshire
Authors: Sparks B. W. 
Published: May 2009

AbstractExamination of material from this locality kept in the Sedgwick Museum since 1881 has revealed much more about its molluscan fauna, especially about the frequency of species. It seems to have been a deposit of the main river Cam in the middle of the Last Interglacial.
The Graptolitic Mudstone and Associated Facies in the Silurian Strata of the Howgill Fells
Authors: Rickards R. B. 
Published: May 2009

AbstractThe graptolitic mudstones, which constitute an important facies of the Silurian strata of the region, are described, and their evolution in time is considered to reflect gradually changing conditions in the depositional environment. The associated facies are discussed and, where possible, their roles assessed.
The Late Pre-Cambrian Stratigraphic Sequence in the Scandinavian Mountain Chain
Authors: Hernes I. 
Published: May 2009

AbstractA late Pre-Cambrian eugeosynclinal stratigraphic sequence in the western part of the Scandinavian mountain chain is established. In the Möre region the succession is about 11 km thick. The wellknown late Pre-Cambrian miogeosynclinal sequence in the eastern part of the chain corresponds to the upper part of the eugeosynclinal sequence.
The London Clay Surface in Part of Suffolk
Authors: Carr A. P. 
Published: May 2009

AbstractThe pre-Pliocene sub-aereal surface of the London Clay in the Orford area of Suffolk is discussed. It is shown that south of Aldeburgh the slope of the London Clay towards the north must be less than previously thought and that prior to the deposition of the Coralline Crag a major river ran approximately from south to north in the area studied. This river course may help to explain the sudden drop of the London Clay surface north of Aldeburgh which has not been fully accounted for previously.
Range, proportionate representation, and demise of brachiopod families through Permian Period
Authors: Waterhouse J. B. , Bonham-Carter G. 
Published: May 2009

SummaryThe time range and proportional distributions of Permian brachiopod families are summarized for the Permian Period. The ‘imperfection’ of the record is calculated from the apparent absences of families known to have survived. It is shown that the phylum changed in composition during the late Middle and Late Permian, with increased importance of Orthida, Strophalosiacea, and Oldhaminida at the expense of the Productacea. Changes were over-printed by loss of families, markedly later than the extensive contraction of shelf-seas, concurrent probably with significant changes in geo chemistry and trophic resources. A number of highly significant families survived into the time of renewed transgression during the Otoceras and Ophiceras ammonoid zones, usually classed at the base of the Triassic Period. The demise of most Permian families proceeded in concert with climatic changes, but the initial deaths of families appear to have been caused by some other unknown factor, which may have severely disrupted Permian communities and biomes, and caused them to respond more than usual to climatic oscillations.
Isotopic age data from Scourian intrusive rocks on the Isle of Barra, Outer Hebrides, north-west Scotland
Authors: Francis P. W. , Moorbath S. , Welke H. J. 
Published: May 2009

SummaryRubidium–strontium and potassium–argon measurements on Lewisian intrusive rocks, considered to be late Scourian in age on general geological grounds, have indeed yielded dates in the range 2450–2600 m.y. This demonstrates that rocks of Scourian age that have escaped substantial Laxfordian reworking are preserved in the Eastern Gneisses of Barra. The relevant geological consequences and correlations are briefly discussed. A cross-cutting late pegmatite yields a typical Laxfordian date of 1679 m.y.
Petrogenesis of Cenozoic sediments of north-western Himalayas
Authors: Chaudhri R. S. 
Published: May 2009

SummaryCenozoic rocks of north-western Himalayas (excluding the sub-Recent, Recent and Karewa deposits) are represented by the Subathu, Dagshai, Kasauli and Siwalik rocks, which together have a thickness of over 10,000 m and range in age from Upper Palaeocene to Middle Pleistocene. From field and laboratory investigations it is propounded that these sediments, except the Middle and Upper Siwalik, have been derived from low and medium grade metamorphic rocks, acid plutonics and sedimentary rocks of the nearby Himalayan terrains. For the Middle and Upper Siwalik rocks, detritus was supplied by sedimentary and trap rocks as well as by the underlying medium and high grade metamorphic and plutonic rocks. A major part of these sediments has been derived from the rising Himalayas rather than from the Peninsular Shield as believed hitherto. The Subathu rocks were deposited in shallow to moderately deep marine environments; the Dagshai rocks under shallow freshwater conditions; and the Kasauli and Siwalik rocks in a shallow fast-sinking basin. All these sediments accumulated under conditions of rapid erosion, short transportation and rapid deposition.
A Tertiary thrust fault on the southern margin of the Bovey Basin
Authors: Bristow C. M. , Hughes D. E. 
Published: May 2009

SummaryGeological investigations and borehole drilling on the southern margin of the Bovey basin around Mainbow ball clay mine and Ringslade open pit have shown that Devonian slate up to 30 m thick is superimposed on Tertiary sediments. A drag fold beneath the slate indicates that the slate has moved eastwards over the Tertiary material. As the slate is relatively intact and not disaggregated, hillcreep cannot be responsible for the superimposition. A large landslip involving a rotational shear cannot be responsible, as the movement plane dips into the hill over too large an area. The southern margin of the Bovey basin is therefore interpreted as a thrust fault of Tertiary age, with thrust plane dipping 10° to 30° S.
It is suggested that this is a rejuvenation of the Variscan thrust recognized in the Bickington area and further west in the Holne area and that the movement on the Tertiary thrust is related to the dextral wrench movement on the Sticklepath fault.
The origin of the Kunavaram amphibolites, Khammam District, Andhra Pradesh, India
Authors: Subbarao K. V. 
Published: May 2009

SummaryChemical and modal analyses of five Kunavaram amphibolites, together with mineralogical data on the pyroxenes and amphiboles, are given. Using petrochemical plots based on Niggli numbers, the trends of variation suggest an igneous origin.
The structure and intrusive mechanism of the Kap Edvard Holm layered gabbro complex, East Greenland
Authors: Elsdon R. 
Published: May 2009

SUMMARYThe complex can be divided into three units, here named the Lower, Middle and Upper Layered Series respectively, on the basis of petrochemical data and correction of the dips of the layering for the effects of post-consolidational flexuring. There are no chilled margins, and the contact with the country rock consists of granular basic and ultrabasic rocks, older than the cumulates of the layered series. The intrusive mechanism is considered in the light of field and chemical data.
Stromatolites from the Middle Old Red Sandstone of Western Orkney
Authors: Fannin N. G. T. 
Published: May 2009

SUMMARYThe structures are comparable with stromatolites seen in modern “flats” environments and tufa occurring in joints in the granite—gneiss basement is compared with modern and fossil forms. Finely laminated (? varved) carbonates with a large lateral persistency (1: 50,000) are referred to periods of high water level and are believed to show evidence of seasonal algal bloom. The presence of widespread stromatolite structures is consistent with earlier environmental interpretations of the Orkney rocks.