1,720,980 research outputs found
Laminated sediments from the Vrica section (Calabria, S. Italy): evidence for plio-pleistocene climatic change in the Mediterranean region
No full textSix laminated sedimentary units (laminites) from the Vrica section (Calabria, southern Italy) have been analyzed geochemically and micropaleontologically to assess paleoclimatic conditions in this region during the transition from the Pliocene to the Pleistocene. Two laminites formed during the early Pleistocene and one formed immediately below the Pliocene/Pleistocene boundary; all have a greater organic carbon content relative to the surrounding marls. By contrast, three late Pliocene laminites exhibit no significant increase in organic carbon, which indicates that the conditions associated with the formation of these three units were somewhat different than those associated with the formation of the three younger laminites. Stable isotope analyses of planktonic foraminifera from the laminites indicate that all of these units were formed during periods of decreased salinity concentrations in surface waters. The laminites were formed as a result of basin anoxia brought on by increased surface-water stratification during periods of high runoff. The Vrica planktonic foraminiferal census data indicates that the laminites contain a distinctive fauna which can be partially attributed to increased nutrient concentrations. By contrast, species assemblages within the marls seem to be primarily controlled by surface-water temperatures. Through the use of polytopic vector analysis, the foraminiferal census data can be simplified into five assemblages, each of which reflects temperature, salinity and/or nutrient concentrations. The nutrient-dependent assemblage indicates an intensification in surface water productivity during periods of laminite formation during the later Pliocene and early Pleistocene, while the temperature-dependent assemblages indicate an overall cooling of surface-water temperatures during the same period. The results of the planktonic foraminiferal analyses support the concept of a regional cooling across the Pliocene/Pleistocene boundary in the Mediterranean. In addition, the results of this study indicate that these climatic changes resulted in differences in the nature of the laminites. Cooler climatic conditions during the latest Pliocene and the early Pleistocene favored the formation of laminites slightly richer in organic carbon and nitrogen because of increased organic carbon input or enhanced organic matter preservation. The warmer climatic conditions of the late Pliocene produced laminites relatively poor in organic carbon and nitrogen as a result of either decreased runoff or decreased organic matter preservation. © 1990
An overview of the post-Messinian paleoenvironmental history of the Western Mediterranean
No full textA review of the Pliocene-Pleistocene paleoenvironmental history of the western Mediterranean is presented based on micropaleontological and geochemical studies of Ocean Drilling Program (ODP) leg 107 material and marine outcrops in southern Italy. The early Pliocene period in the Mediterranean was marked by relatively high-amplitude climatic oscillations. In marginal areas, these climatic oscillations resulted in the rhythmic deposition of limestone-marl couplets which have an average duration of approximately 19 000 years. The global cooling at ~2.4 Ma and the associated expansion of northern hemisphere glaciation resulted in a shift to more arid conditions in the Mediterranean region. The δ18O record for site 653 is marked by a sharp cooling across the Pliocene/Pleistocene boundary
Chronology of the pleistocene oxygen isotope record: 0–1.88 m.y. B.P
No full textDetailed oxygen isotope records from various ocean basins and representing the last 1.88 m.y. are correlated using nannofossil biostratigraphy and paleomagnetic stratigraphy. These correlations establish the global nature of oxygen isotope stages 23 through 63 in the early Pleistocene to latest Pliocene. A composite isotope record for the last 1.88 m.y. reveals that the mid-Pleistocene change in climate regime was a complicated response that lasted from approximately 0.9 to 0.6 Ma and not a simple shift from one climate mode to another. The proposed chronology for the extended isotope stages provides a chronostratigraphic framework for detailed studies of paleoceanographic processes in the early Pleistocene and paves the way for application of oxygen isotope stratigraphy to early Pleistocene deep-sea and continental margin drilled sections. © 198
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
Detachment faulting and late Paleozoic epithermal Ag-base-metal mineralization in the Spanish central system
No full text4 páginas.Hydrothermal activity during late Hercynian time resulted in epithermal silver-base-metal (Pb-Zn-Cu) vein formation in the eastern part of the Spanish central system. During the Hercynian orogeny, the central Iberian crust was thickened by compressional tectonics, heated, weakened, and subsequently overthickened by massive late Hercynian granitic intrusions. Subsequently, the central Iberian crustal welt underwent extensional collapse through lithosphere-scale, low-angle detachment faulting. The detachment systems evolved through tectonic denudation, isostatic rebound, and upward arching to define an extensional province much like the U.S. Basin and Range. Andesitic volcanism and hydrothermal activity occurred during extension, inducing epithermal-type hydrothermal convecting systems that leached, transported, and precipitated silver and base metals along fractures crosscutting the Hiendelaencina metamorphic core complex.Peer reviewe
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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