bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sedimentation and tectonism in the Middle Ordovician of the Girvan district, SW Scotland
Authors: Ince David 
Published: November 2011

ABSTRACTThe Kirkland Conglomerate and the Benan Conglomerate and associated sediments of the Barr Group (Ordovician—Llanvirn-Llandeilo) of the Girvan district, SW Scotland record the development of two fan-delta systems situated on the northern margin of Iapetus. The intervening Stinchar Limestone represents a shallow marine fan-delta abandonment facies. Subaerial fan-delta deposits are seen at the lowest exposed horizons within the Kirkland Conglomerate. Transgression and eventual abandonment of the fan-delta system is recorded by (1) matrix-rich gravels forming the topmost horizons of the unit. (2) subaqueous distributary channel sands of the overlying transitional sandstone and associated shallow-marine carbonates of the Auchensoul Limestone and (3) shallow-marine sandstones of the Confinis Flags. Following a period of shallow-water sedimentation (Stinchar Limestone), a phase of rapid subsidence occurred during the upper Llandeilo, broadly synchronous with theNemagraptus gracilisZone transgression. Lowermost horizons of the succeeding Benan Conglomerate comprise re-sedimented gravels and laterally equivalent ‘outer shelf’ deposits (Superstes Mudstone). Renewal of coarse clastic sedimentation resulted from source area uplift related to granite plutonism, responsible also for the rapid subsidence of basinal areas. Fan-delta progradation is recorded by the occurrence of braided-fluvial deposits and shallow-marine carbonates at higher stratigraphical levels within the unit. Progradation of the fan-delta complex resulted from a gradual reduction in subsidence rates along basin-margin faults.Fan-deltas of the Barr Group prograded southwards, from a SW—NE-trending faultdelineated basin margin, across a narrow shelf area. To the S of the shelf area defined by Barr Group outcrop, sediments of the Tappins complex accumulated in outer shelf, ?slope and base of slope settings.The thickness of individual conglomerate units (>150 m—Kirkland Conglomerate, and up to 700 m—Benan Conglomerate), the associated high sedimentation rates, narrowness of the shelf area, and distribution and style of basin-margin faults indicate that oblique-slip motion along the northern margin of Iapetus may have provided a major control over Middle Ordovician sedimentation in the Girvan district.
Lower Ordovician brachiopods from the Ben Suardal Limestone Formation (Durness Group) of Skye, western Scotland
Authors: Curry Gordon B. , Williams Alwyn 
Published: November 2011

ABSTRACTTen silicified brachiopod taxa have been recovered from the Ben Suardal Limestone Formation (Durness Group) on the Isle of Skye, western Scotland. This Arenig fauna contains a new camerellid genus, Boreadocamara, and new species of each of the orthacean genera Archaeorthis, Fasciculina, and Oligorthis. Representatives of Billingsella, Finkelnburgia, Syntrophia, Syntrophopsis, and an indeterminate orthacean have also been recovered from etched residues of the Ben Suardal Limestone. The Skye fossils show strong affinities with the Scoto-Appalachian or American faunal province, in keeping with the inferred plate tectonic position of the Durness Group along the northwestern margin of the early Palaeozoic ‘Iapetus’ Ocean.
Granite emplacement mechanisms and tectonic controls: inferences from deformation studies
Authors: Hutton Donald H. W. 
Published: November 2011

ABSTRACTThis paper is a structural and tectonic approach to the emplacement and deformation of granitoids. The main methods available in structural geology are briefly reviewed and this emphasises that (a) a wealth of data, particularly strain and shear sense, which pertain to these problems, can be determined in and around plutons; (b) given the nature, unlike many other crustal rock types, of granites to crystallise from isotropic through weakly anisotropic crystal suspension fluids, that deformation which has occurred in these states may not be well preserved; and (c) it is entirely possible, using this methodology, to separate deformation resulting from externally originating tectonic stresses from that which is associated with internal magma-related stresses. It is also recommended that the genetically-based Cloosian classification of granite fabrics and structures into “primary” (magmatic flow/magmatic flow current) and “secondary”, be abandoned and that a more observationally-based approach which classifies granite deformation fabrics and structures according to their time of occurrence relative to the crystallisation state of the congealing magma, be adopted (i.e. pre-full crystallisation deformation and crystal plastic strain deformation).Examples of recent, structurally based, studies of emplacement mechanisms of plutons within tectonic settings are described and these show that, in general, space for magma can be created by the combination of tectonically-created cavities and internal magma-related buoyancy. This occurs in both transcurrent and extensional tectonic settings and there is no reason to doubt that it can happen in compressive-contractional regimes. It is concluded that transient and permanent space creation, such as may be exploited by available magmas, is a typical feature of the tectonically stressed and deforming lithosphere and this, in combination with the natural buoyancy and ascending tendency of magmas, can generate the varied emplacement mechanisms of granites.
Ordovician graptolites from the northern Sierra de Cobachi, Sonora, Mexico
Authors: Riva John F. , Ketner Keith B. 
Published: November 2011

ABSTRACTTwo Ordovician graptolite assemblages are recognised and described for the first time in the allochthonous siliceous assemblage or succession forming the Guayacan Group of central Sonora in northwestern Mexico. A Middle Ordovician assemblage referable to theNemagraptus gracilis-Climacograptus wilsonizonal interval occurs in the upper siliceous shale of unit 1 of the Guayacan Group and an Upper Ordovician assemblage representative of theDicellograptus ornatusZone of the Pacific faunal province has been collected from shaly partings in the bedded radiolarian chert constituting unit 2. The stratigraphical make-up of the siliceous assemblage bears a striking similarity to the better known—and correlative—Lower Palaeozoic siliceous succession of central and northern Nevada, giving credence to the hypothesis that the Palaeozoic siliceous assemblage in northwestern Mexico was originally the extension of the Nevadan assemblage into California, which has been transposed to its present position along a left-lateral megashear of the magnitude of at least 1000 km.A review of the proximal development of the spinose species remaining in the form genusClimacograptusHall has led to the proposal to restrict the genus toClimacograptus bicornis(Hall), its type species, and to two other septate species of early Middle Ordovician age (Llandeilo-early Caradoc) with a primitive type of proximal-end development. The genusEuclimacograptus, withClimacograptus hastatusT. S. Hall as the type species, is proposed for spinose Upper Ordovician climacograptids with an advanced proximal-end development. The genusEnsigraptus, withClimacograptus caudatusLapworth as the type species, is also proposed for species homeomorphic with those included inNormalograptusLegrand but with a less advanced proximal-end development. Five species are described.
A palaeoenvironmental interpretation of the Silurian rocks in the Pentland Hills, near Edinburgh, Scotland
Authors: Robertson Gary 
Published: November 2011

ABSTRACTSilurian sediments up to 2500 m thick are exposed in the Pentland Hills, SW of Edinburgh. These sediments, the North Esk Group, are here sub-divided into five well-defined formations: the Reservoir Formation, Deerhope Formation, Cock Rig Formation, Wether Law Linn Formation and Henshaw Formation. The Wether Law Linn Formation is further sub-divided into three members. Based on limited palaeontological evidence, the sediments appear to be late Llandovery (crenulata Biozone) to Wenlock in age. The Silurian sediments represent a regressive sequence, passing from offshore submarine-fan turbidite facies, through shallow marine sediments, with an abundant flora and fauna, possibly a barrier complex, to terrestrial red beds of Old Red Sandstone facies. Changing faunal associations in the shallow marine sediments reflect the availability of different substrates. The regression occurred on the southern margin of the Midland Valley graben.
Correlation of depositional sequences in a structurally complex area: the Dalradian of Glenn Fearnach to Glen Shee, Scotland
Authors: Goodman S. , Crane A. , Krabbendam M. , Leslie A. G. , Ruffell A. 
Published: November 2011

ABSTRACTThe stratigraphy of the Neoproterozoic Dalradian Supergroup has been formalised at group, subgroup and formation level, based largely on mapping in the SW Highlands of Scotland. Elsewhere, there has been a tendency for the lithostratigraphy to be fitted into this framework, implying that the lithostratigraphy represents basin-wide changes in depositional environment. The pitfalls of this ‘layer-cake’ approach are illustrated by interpreting the geology of the Gleann Fearnach to Glen Shee area of the Central Highlands, using the published maps of the adjacent regions. Attempts to correlate units into the Braemar area in the NE and into the Pitlochry area in the SW show considerable mismatch between the maps covering these areas, which has in the past led to invocation of geometrically unlikely arrangements of faults and slides to explain the lithostratigraphical distribution.The present study is the result of a different approach adopted during remapping of the Gleann Fearnach to Glen Shee area. Some basin-wide events, here suggested to be associated with key sequence stratigraphic surfaces, were identified. These principally relate to the deposition of Appin Quartzite, Boulder Bed and Ben Lawers Schist precursor sediments. Between these reference units the stratigraphy has been determined by detailed field mapping, and variation from the standard stratigraphy explained in terms of both the position within the depositional sequence and palaeogeography during deposition. This has led to an integrated solution which works on both sedimentological and structural grounds. There are local implications for the stratigraphy and structural geology elsewhere in the Scottish Dalradian, but, more importantly, it is an approach which must be more widely applied in order to make wider correlations beyond the British Dalradian to the rest of the Laurentian margin.
Trilobites from the Ordovician Ardwell Group of the Craighead Inlier, Girvan district, Scotland
Authors: Tripp R. P. 
Published: November 2011

ABSTRACTAll trilobites known from the Ardwell Group, Craighead Inlier, Girvan district are listed and frequencies recorded.Encrinuroides lapworthin. sp. from the Sericoidea Mudstones, andBumastoides fornaxn. sp. from the Kiln Mudstones, are described. The Sericoidea Mudstones constitute a deeper water interlude in the complex succession which comprises the Craighead Limestone Formation; graptolites from this horizon indicate lowDicranograptus clinganizone. The closest resemblance of the trilobite assemblage as a whole is to faunas of Trenton age in North America. The occurrence of forms allied to Boda Limestone (Ashgill) species suggests that these are long-ranging, carbonate associated, trilobite stocks.
Magnetic susceptibility record of Chinese Loess
Authors: Kukla G. , An Z. S. , Melice J. L. , Gavin J. , Xiao J. L. 
Published: November 2011

ABSTRACTRecords of the low field magnetic susceptibility at three sites in the Chinese Loess Plateau, each with sediments covering the last 2·5 Ma, were averaged and combined into a single stacked file whose dating is independent of astronomic chronology. The stack reveals orbital frequencies, which are in general agreement with the astronomically tuned oxygen isotope deep sea chronology in the upper part of the Brunhes epoch, but disagree prior to 0·5 Ma ago.
The Laurentide ice sheet through the last glacial cycle: the topology of drift lineations as a key to the dynamic behaviour of former ice sheets
Authors: Boulton G. S. , Clark C. D. 
Published: November 2011

ABSTRACTStudy of satellite images from most of the area of the Canadian mainland once covered by the Laurentide ice sheet reveals a complex pattern of superimposed drift lineations. They are believed to have formed subglacially and parallel to ice flow. Aerial photographs reveal patterns of superimposition which permit the sequence of lineation patterns to be identified. The sequential lineation patterns are interpreted as evidence of shifting patterns of flow in an evolving ice sheet. Flow stages are recognised which reflect roughly synchronous integrated patterns of ice sheet flow. Comparison with stratigraphic sections in the Hudson Bay Lowlands suggests that all the principal stages may have formed during the last, Wisconsinan, glacial cycle. Analogy between Flow stage lineation patterns and the form and flow patterns of modern ice sheets permits reconstruction of patterns of ice divides and centres of mass which moved by 1000–2000 km during the glacial period. There is evidence that during the early Wisconsinan, ice sheet formation in Keewatin may have been independent of that in Labrador–Quebec, and that these two ice masses joined to form a major early Wisconsinan ice sheet. Subsequently the western dome decayed whilst the eastern dome remained relatively stable. A western dome then re-formed, and fused with the eastern dome to form the late Wisconsinan ice sheet before final decay.Because of strong coupling between three-dimensional ice sheet geometry and atmospheric circulation, it is suggested that the major changes of geometry must have been associated with large scale atmospheric circulation changes.Lineation patterns suggest very little erosional/depositional activity in ice divide regions, and can be used to reconstruct large scale patterns of erosion/deposition.The sequence of flow stages through time provides an integrative framework allowing sparse stratigraphic data to be used most efficiently in reconstructing ice sheet history in time and space.
Time-scales and degrees of freedom operating in the evolution of continental ice-sheets
Authors: Hindmarsh Richard C. A. 
Published: November 2011

ABSTRACTComprehensible explanations of the operation of earth climate systems should consist of descriptions of the operation of a few degrees of freedoms. Qualitative interpretations of results from large-scale numerical models generally follow this principle, but do not render formal definitions of the precise nature of such degrees of freedom.At its simplest, ice-sheet kinematics requires knowledge of the evolving height and span. Rheology and surface mass-balance impose different requirements upon the co-evolution of these variables, meaning a two-degree of freedom model is over-prescribed. By means of a perturbation expansion about the analytic similarity solution for viscous spreading, eigenfunctions corresponding to degrees of freedom in the ice-sheet profile are obtained, and are used to decompose mass-balance distributions. Only a few eigenfunctions are needed to replicate numerical models, implying that ice-sheets in plane flow may operate with fewer than ten degrees of freedom.Unstable evolution of ice-sheets can occur, when the operation of a very large number of degrees of freedom can be manifested. Previous work is reviewed and new results for the unstable transformation of valley glaciers into ice-sheets are presented. Phasing of initiation may be an unpredictable phenomenon.
The petrology of the Lugar Sill, SW Scotland
Authors: Henderson C. M. B. , Gibb F. G. F. 
Published: November 2011

ABSTRACTA 49 m complete section through the 288 Ma Lugar Sill obtained from drill cores can be subdivided into nine units. The uppermost four units are teschenitic and are mirror images of the bottom four. A 35 m thick central unit consists of theralite passing down into kaersutite theralite and then picrite. Marginal chilling 'of the units indicates multiple intrusion from the outside inwards. Olivine in the central unit (Fo88–90) encloses Cr-rich spinels and increases in amount inwards to over 50%. Clinopyroxene, kaersutite and biotite show symmetrically increasing Fe/Mg from the centre of the sill outwards. Most major and trace elements vary symmetrically throughout the sill with those in the central unit reflecting mainly olivine distribution but incompatible elements exhibit upward enrichment. Remarkably, the most-evolved rocks in the sill are at its margins. The sill was formed by multiple injections of successivelyless-evolved teschenitic magmas followed by a larger pulse of theralitic liquid carrying abundant olivine phenocrysts. The amount of olivine in this final pulse increased during emplacement. Subsequentin-situdifferentiation in the central unit, with upward enrichment in residual liquid and volatiles, gave rise to lugarites. The various magmas were produced in a lower-level magma chamber by differentiation of a mantle-derived, alkali-rich picritic magma.
Permian K-rich volcanic rocks of Devon: petrogenesis, tectonic setting and geological significance
Authors: Thorpe R. S. 
Published: November 2011

ABSTRACTPotassium (K)-rich volcanic rocks occur within Permian sedimentary rocks in SW England and are approximately contemporaneous with the emplacement of the Cornubian granite batholith. The volcanic rocks have chemical characteristics of subduction-related magmas and may have been derived by small amounts of partial melting of heterogeneous large-ion lithophile (LIL) enriched mantle with the assemblage olivine–pyroxene–garnet–phlogopite–titanate. The LIL enrichment may have occurred during shallow or oblique subduction of oceanic lithosphere below SW England during the Devonian and Carboniferous. Such LIL-enriched mantle may have contributed some components to the Cornubian granite batholith.
Geophysiology
Authors: Lovelock James E. 
Published: November 2011

ABSTRACTThe geological theory of the evolution of the material environment and the biological theory of the evolution of organisms by natural selection are usually treated separately. This paper presents a new evolutionary theory, in which the evolution of the organisms, and the evolution of their material environment, are seen to be so closely coupled as to form a single, indivisible, process. This combined evolutionary system can be taken to be a domain with emergent properties unexpected from a simple addition of its component parts, rather like the eighteenth-century scientific view of the Earth as a super-organism. In homage to James Hutton, who lectured before the Royal Society of Edinburgh about the Earth as a super-organism and on the physiology of the Earth, the new topic is called geophysiology.The difference between the geophysiological view of the Earth, where the environment and the organisms are tightly coupled, and the co-evolutionary, or biogeochemical view, where the coupling is loose leaving organisms and their environment to evolve more or less separately, is discussed. The paper includes numerical models to illustrate how a close-coupled evolutionary system could have self regulation, homeostasis, as an automatic and emergent property. The models will be compared with the real world past and present and their predictions examined.
Environmental controls on the taphonomy and distribution of Carboniferous malacostracan crustaceans
Authors: Briggs D. E. G. , Clarkson E. N. K. 
Published: November 2011

ABSTRACTShrimp-like malacostracan crustaceans first appeared in the late Devonian and underwent a substantial adaptive radiation in the Carboniferous. They are rarely found in rocks of fully marine origin but are well represented in sediments laid down in brackish water and marginal marine conditions; such transitional environments provide the exceptional circumstances required for the preservation of unmineralised shrimps. The best examples are in the Dinantian of Scotland, the Namurian of Montana, and the Westphalian of Illinois. It is probable that shrimps were widespread in contemporaneous marine environments, but are not preserved.Any approach to understanding the physiology of fossil organisms is necessarily indirect. The diversity of crustacean communities, and the nature of associated taxa and trace fossils, are the most useful biotic factors for interpreting the habitat and tolerance of fossil examples.All known Carboniferous crustacean communities lived in brackish conditions; none is fully marine. Malacostracan assemblages in the Dinantian of Britain show a general trend of increasing diversity with salinity, from a single taxon at Gullane (stratified freshwater lake or brackish lagoon) to ten at Glencartholm (approaching normal marine).Tealliocarisis associated with low salinities.Crangopsis socialisis confined to the brackish water interdistributary bay environment, butBairdopsandBelotelsondisplay a broader environmental tolerance.Crangopsis eskdalensis, Sairocaris, andPerimecturusoccur only at Glencartholm, indicating a requirement for a strong marine influence. Those taxa confined to a limited environmental range all occur where a marine influence is pronounced; none occurs solely in areas of lower salinity. While salinity was apparently the dominant influence on distribution, a complex of independently varying environmental factors was involved. The range of habitats colonised early in the Carboniferous indicates that the preserved taxa had already developed advanced osmoregulatory mechanisms.
Mechanics and physiology of flight in fossil vertebrates
Authors: Rayner Jeremy M. V. 
Published: November 2011

ABSTRACTFlight—defined as the ability to produce useful aerodynamic forces by flapping wings—is one of the most demanding adaptations in vertebrates. The mechanical problems of flight ensure considerable external morphological homogeneity and behavioural similarity in extant fliers. Observations of the vortex wakes and wingbeat geometry of modern birds and bats confirm that the two groups are mechanically very similar, despite differences in phylogeny, anatomy and physiology. With this background it is possible to attack two problems: the evolution of flight in vertebrates, and the flight performance of extinct animals such as pterosaurs andArchaeopteryx.The origin of flight has been surrounded by considerable controversy, due in part to terminological inconsistencies, in part to phylogenetic uncertainty over the relationships of birds, bats and pterosaurs, in part to disagreement over the interpretation of the available fossil evidence, and in part to argument over the relative importance of morphological, mechanical and ecological specialisations. The mechanical changes needed in the course of the evolution of flight favour a gliding origin of tetrapod flight, and on mechanical and ecological grounds the alternative cursorial hypothesis may be discounted. This argument is particularly strong in bats, but has been thought to be weaker in birds owing to apparent inconsistencies with the fossil evidence. However, fossils of the Jurassic theropod dinosaurArchaeopteryxalso support a gliding origin for flight, and suggest that this animal was adapted for flapping flight at moderately high speeds associated with gliding; it could fly less well at the slow speeds which would have been required for incipient flight in a running cursor, and at which the wingbeat is aerodynamically and kinematically considerably more complex. Slow flight in birds and bats is the more derived condition, and vertebrate flapping flight apparently evolved through a gliding stage.The pterosaurs have become the subject of much controversy over the nature of their stance, the wing surface, and the degree of involvement of the leg in the wing membrane. Reconstruction of their wings indicates proficient flying animals, and comparison with birds suggests that most pterosaurs probably occupied marine or coastal/estuarine habitat.