1,721,091 research outputs found
Early Cretaceous dendritic shrub-like fabric in karstified peritidal carbonates from southern Italy
No full textLower Cretaceous (Valanginian) dendritic microfabrics occur in karstic cavities within fine-grained shallowmarine
platform carbonates at San Lorenzello, southern Italy. They form dense micritic masses and clusters,
generally oriented perpendicularly to cavity surfaces, surrounded by layered sparry cement. Individual dendrites,
typically sub-millimetric in size, have highly irregular margins and form distinctive shrub-like masses ranging
from compact and squat, to elongate and highly branched. The centimetric and irregularly elongate cavities
appear to have formed through subaerial exposure, and are almost entirely filled by the micritic dendrites and
associated sparry crusts. In size, shape and micritic composition, the dendrites broadly resemble a variety of
similar fabrics, including hot spring travertine shrubs and calcified microfossils such as Cambrian Angusticellularia,
which has analogs in present-day lacustrine calcified cyanobacteria. However, the San Lorenzello dendrites differ
in occupying small cavities. This cryptic microkarstic dripstone setting, together with the often regular spacing
and appearance of these dendritic fabrics, may be more consistent with an abiotic origin. These comparisons underscore
the challenge of interpreting microdendritic carbonates fabrics in general
Petrographic and geochemical evidence of bacterial activity in Messinian carbonates from the Sutera section, Caltanissetta Basin, Sicily
No full textAncient trace of life in hypersaline environment recorded in the Messinian Calcare di Base Formation from Sutera, Caltanissetta Basin, Sicily
No full textCarbonate stromatolites from a Messinian hypersaline setting in the Caltanissetta Basin, Sicily: petrographic evidence of microbial activity and related stable isotope and REE signatures
No full textLower Messinian stromatolites of the Calcare di Base Formation at Sutera in Sicily record periods of low sea-level, strong evaporation and elevated salinity, thought to be associated with the onset of the Messinian Salinity Crisis. Overlying aragonitic limestones were precipitated in normal to slightly evaporative conditions, occasionally influenced by an influx of meteoric water. Evidence of bacterial involvement in carbonate formation is recorded in three dolomite-rich stromatolite beds in the lower portion of the section that contain low domes with irregular crinkly millimetre-scale lamination and small fenestrae. The dominant microfabrics are: (i) peloidal and clotted dolomicrite with calcite-filled fenestrae; (ii) dolomicrite with bacterium-like filaments and pores partially filled by calcite or black amorphous matter; and (iii) micrite in which fenestrae alternate with dark thin wispy micrite. The filaments resemble Beggiatoa-like sulphur bacteria. Under scanning electron microscopy, the filaments consist of spherical aggregates of dolomite, interpreted to result from calcification of bacterial microcolonies. The dolomite crystals are commonly arranged as rounded grains that appear to be incorporated or absorbed into developing crystal faces. Biofilm-like remains occur in voids between the filaments. The dolomite consistently shows negative d13C values (down to -11.3‰) and very positive d18O (mean value 7.9‰) that suggest formation as primary precipitate with a substantial contribution of organic CO2. Very negative d13C values (down to -31.6‰) of early diagenetic calcite associated with the dolomite suggest contribution of CO2 originating by anaerobic methane oxidation. The shale-normalized rare earth element patterns of Sutera stromatolites show features similar to those in present-day microbial mats with enrichment in light rare earth elements, and M-type tetrad effects (enrichment around Pr coupled to a decline around Nd and a peak around Sm and Eu). Taken together, the petrography and geochemistry of the Sutera stromatolites provide diverse and compelling evidence for microbial influence on carbonate precipitation
Fossil microbial events in the Messinian Calcare di Base Formation from Sutera, Caltanissetta Basin, Sicily
No full text
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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