1,721,029 research outputs found
Global Carboniferous brachiopod biostratigraphy
No full textWe present an updated look at Carboniferous brachiopod biozonation from most of the world framedinto a revised Carboniferous palaeogeography, based on a selection of the literature published on Carboniferousbrachiopods since the nineteenth century. The biostratigraphic significance of the most important brachiopodtaxa is synthesized in seven geographical correlations.The Mississippian is characterized by rich brachiopod faunas, with widespread taxa with a good potential forglobal correlation, such as Rugosochonetes, Delepinea, Buxtonia, Antiquatonia, Spinocarinifera, Marginatia,Fluctuaria, Ovatia, Rhipidomella, Lamellosathyris, Unispirifer, Tylothyris and Syringothyris.From the mid-Visean to the late Serpukhovian, taxa of gigantoproductidines are biostratigraphically significant,and occur everywhere except South America and Australia, which remain as distinct faunal successions formost of the period. A major turnover occurs at the beginning of the Pennsylvanian, characterized by a higherdegree of provincialism. Pennsylvanian brachiopod faunas are diverse in China, Russia and North America, butotherwise they are less developed and are characterized mostly by endemic taxa, hampering long-distance correlation.An exception is the rapid diversification of taxa of the Choristitinae, which were widespread from theBashkirian to the Moscovian, allowing long-distance correlation.Fil: Angiolini, Lucia. Università degli Studi di Milano; ItaliaFil: Cisterna, Gabriela Adriana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; ArgentinaFil: Mottequin, Bernard. Royal Belgian Institute of Natural Sciences; BélgicaFil: Shen, Shu-Zhong. Nanjing University; ChinaFil: Muttoni, Giovanni. Università degli Studi di Milano; Itali
The paradox of the end Permian global oceanic anoxia
No full textGeochemical results argue against global anoxia as a or the cause for the end Permian mass extinction. Instead, they suggest that the water column was oxic and sometimes the sediment pore water was suboxic, which is the norm. Anoxia, if present, may reflect local conditions developed in deep water settings, but that have to be supported by concrete and direct evidence
METHANE HYDRATE: KILLER CAUSE OF EARTH’S GREATEST MASS EXTINCTION
No full textThe cause for the end Permian mass extinction, the greatest challenge life on Earth faced in its geologic history, although still hotly debated it bears an important message for humanity. The most significant marker of this event is the negative δ13C shift and rebound recorded in marine carbonates with a duration ranging from 2000 to 19,000 years. Leading cause for the event are Siberian trap volcanism and its emission of greenhouse gases with consequent global warming, but other leading contenders are oceanic anoxia and acidification. We present measurements of gases vaulted in shell calcite of end Permian brachiopods and whole rock, documenting significant differences in normal atmospheric equilibrium concentration (NAEC) of gases between modern and end Permian seawaters. The gas composition recorded in end Permian brachiopod gas-inclusions reflects dramatically higher seawater methane contents leading up to the event. Initial global warming of 8 to 11°C sourced by isotopically light carbon dioxide from volcanic emissions triggered the sudden release of methane from permafrost and shelf sediment hydrate. Consequently, the huge quantities of methane emitted into the atmosphere and the oceans accelerated global warming and marked the negative δ13C spike observed in marine carbonates marking the onset of the biggest mass extinction in Earth history. The rapidity of the methane emission lasting from several years to thousands of years was tempered by the equally rapid oxidation of the atmospheric and oceanic methane that gradually reduced its warming potential but not before global warming had reached levels lethal to most life on land and in the oceans. Based on measurements of gases trapped in biogenic and abiogenic calcite, the release of methane (of ~ 8 -28 % of total C stored) from permafrost and shelf sediment hydrate was the ultimate source and cause for the dramatic life-changing global warming (GMAT > 34°C) and oceanic (negative carbon isotope excursion) changes observed during the end Permian. Global warming triggered by the exorbitant release of carbon dioxide may be catastrophic, but the subsequent release of methane hydrate may be apocalyptic. The end Permian may have an important lesson for humanity regarding the issue of global warming and climate change it faces today
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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