1,720,979 research outputs found
Katian conodonts from the Portrane Limestone: the first Ordovician conodont fauna described from Ireland
No full textThe Portrane Limestone, which crops out in a small inlier about 17 km north of Dublin, is one of the few significant carbonate units in the Ordovician of Ireland. Samples from this formation, which has long been famous for its diverse silicified shelly fauna, have produced a biostratigraphically diagnostic conodont fauna of more than 2200 specimens representing a total of 26 taxa. The Amorphognathus superbus and A. ordovicicus zonal conodont species have been documented. Our study, the first one illustrating diverse assemblages of Ordovician conodonts from Ireland, shows that this fauna, which represents the Hamarodus brevirameus-Dapsilodus mutatus-Scabbardella altipes biofacies, is strikingly similar to middle Katian (Stage Slice Ka3) faunas from Wales, England, and continental Europe. This age dating is consistent with that advocated based on shelly fossils. The Portrane Limestone was deposited in a volcanic arc environment off the Avalonian microcontinent and is now located southeast of the Iapetus suture across Britain and Ireland. The fact that the Portrane area was placed on the southeastern side of the Iapetus and relatively close to Wales and northern England but probably widely separated from North America, may at least partly explain why the Portrane conodont fauna differs in important respects from broadly coeval faunas from eastern North America and has much closer affinities with European faunas
Silurian agglutinated foraminifera from the Dingle Peninsula, Ireland
No full textViene qui descritta per la prima volta una associazione di foraminiferi agglutinanti all’interno di calcari siluriani della Penisola di Dingle, Contea di Kerry, Irlanda sud-occidentale. La collezione è stata rinvenuta nel residuo di campioni trattati per la preparazione di conodonti. I foraminiferi sono dominati da tubotalamidi (Rectoammodiscus e rari Sansabaina), mentre più rari sono i monotalamidi (Psammosiphonella e Psammosphaera). A livello speci co l’associazione presente in Irlanda è identica a quella descritta in precedenza nel Siluriano del Nord America, anche se presenta minore diversità. Tutte le specie rinvenute hanno una lunga distribuzione stratigra ca, e quindi ricoprono un signi cato limitato per correlazioni stratigra che. La fauna a conodonti ritrovata nei campioni ha permesso una attribuzione dei foraminiferi agglutinanti alla parte iniziale del Ludlow.An assemblage of primitive agglutinated foraminifera is reported for the first time from Silurian limestones from the Dingle Peninsula, Ireland. The assemblage is dominated by tubothalamids (Rectoammodiscus and rare Sansabaina), with less abundant monothalamids (Psammosiphonella and Psammosphaera). At the species level, the agglutinated foraminiferal assemblage is identical to those described previously from the Silurian of North America but is of lower diversity. The foraminiferal assemblage has limited potential for stratigraphic correlation as long-ranging taxa are present. The co-occurring conodont fauna enables an assignment to the early Ludlow
An investigation of the fluids involved in the formation of some Irish lower carboniferous dolomites
No full textTHESIS 7431Irish Carboniferous rocks are host to an abnormally large amount of lead/zinc mineralisation and are internationally important in studies of the genesis of carbonate- hosted lead/zinc deposits. The host to mineralisation at Lisheen and Galmoy, the two most recently discovered commercial Zn-Pb deposits, is dolomitised late Toumaisian Waulsortian Limestone. This association between dolomite and base-metal sulphides has stimulated much research into the nature of the fluids responsible for the dolomitisation and the relation of dolomitisation to mineralisation. This study provides a more detailed examination of several dolomitised sections throughout the Irish Midlands, both within and outside the main mineralised zone, than carried out to date, in an effort to reconstruct their diagenetic and fluid flow history. Dolomitisation post-dated the final porosity occlusion within the precursor limestone in all of the areas studied. Fine-grained grey dolomite occurred during the initial stages of dolomitisation and commonly selectively replaced the micrite and bryozoan material. Replacement by this dolomite was generally mimetic. Texturally later coarse-grained white dolomite has a similar luminescence to the fine-grained dolomite and is both a replacive and open space-filling dolomite. Replacement by this dolomite is non-mimetic, with the dolomite crystals being orders of magnitude greater than the precursor calcite phase. At least during the initial stages of dolomitisation dissolution seams may have been exploited as conduits, enabling the Mg bearing fluids to move through the well-cemented limestone
The use of dissociated crinoid ossicles as biostratigraphical and palaeoecological tools in the Carboniferous of northwest Ireland
No full textTHESIS 6366.1THESIS 6366.2Fossil crinoids were investigated from the Lower Carboniferous (Visean) rocks of northwest Ireland. In this area the deltaic Mullaghmore Sandstone Formation stratigraphically separates the Bundoran Shale Formation (Arundian) and the Benbulben Shale Formation (Holkerian-Asbian). These two formations are similar lithologically consisting of clay-rich, calcareous shale interbedded with discontinuous beds, and lenses of bioclastic, often argillaceous limestone. The sedimentary sequence represents the incursion of a fluviodeltaic complex into the Carboniferous sea of northwest Ireland and its subsequent retreat. The Bundoran Shale Formation records the progradation of the delta over prodelta muds, and the Benbulben Shale Formation represents a major flooding surface on the subsequent receding delta. Although several horizons throughout the succession have been sampled, the study concentrated particularly on these two formations since they yielded countless fossil crinoid specimens
Potential evolutionary trade‐off between feeding and stability in Cambrian cinctan echinoderms
Full text linkReconstructing the function and behaviour of extinct groups of echinoderms is problematic because there are no modern analogues for their aberrant body plans. Cinctans, an enigmatic group of Cambrian echinoderms, exemplify this problem: their asymmetrical body plan differentiates them from all living species. Here, we used computational fluid dynamics to analyse the functional performance of cinctans without assuming an extant comparative model. Three‐dimensional models of six species from across cinctan phylogeny were used in computer simulations of water flow. The results demonstrate that cinctans with strongly flattened bodies produced much less drag than species characterized by dorsal protuberances or swellings, suggesting the former were more stable on the seafloor. However, unlike the flattened forms, cinctans with high‐relief bodies were able to passively direct flow towards the mouth and associated food grooves, indicating that they were capable of more efficient feeding on particles suspended in the water. This study provides evidence of a previously unknown evolutionary trade‐off between feeding and stability in Cambrian cinctan echinoderms
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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