1,721,099 research outputs found
MIS 5e at San Giovanni di Sinis (Sardinia, Italy): Stratigraphy, U/Th dating and “eustatic” inferences
No full textThe most representative Late Pleistocene (“Tyrrhenian”) outcrop in Sardinia (San Giovanni di Sinis) was re-visited based on detailed sedimentological and stratigraphical analysis supported by U-series dating of fossil corals. The stratigraphy shows shoreface–backshore sandstones overlying an erosional surface cut on vertebrate-bearing layers. Facies analysis and sequence-stratigraphic approaches suggest “eustatic” changes during the overall depositional interval of the marine sequence. Disconformities distinguish two coastal units suggesting a lateral shifts of the depositional environments driven by millennial-scale frequency sea level fluctuations, never exceeding a maximum height +1 to +3 m and by a subsequent rise to +5 ÷ +5.5 m asl.
These deposits have historically been assigned to MIS 5, on the basis of i) their palaeontological content (warm “Senegalese” fauna), ii) lithostratigraphic interpretations and iii) amino-acid, geochronological data and generally attributed to the high sea-level episode of MIS 5e sub-stage, through sequential interpretation. U-series measurements in colonies of Cladocora caespitosa from the main outcrop of San Giovanni di Sinis and other minor deposits from the eastern side of the isthmus and from Capo San Marco, yielded 230Th-ages confirming an assignment of the embedding sediments to MIS 5e.
Similar measurements in a pelecypod valve (Cerastoderma sp.) and a vermetid colony at San Marco yielded much younger apparent ages, tentatively attributed to late “diagenetic” U-uptake processes. Both the first minor pulses and the most important “eustatic” pulse recorded at San Giovanni di Sinis cannot be assigned unequivocally to one of the MIS 5e sea-level oscillations proposed in the recent literature, due to dating inaccuracies and uncertainties, but it seems probable that it occurred during an early part of the interval
Further U-Series data from the Late Pleistocene deposits of Capo San Marco (Sardinia): An Open Chemical System Or Evidence For A ~70 Ka High Relative Sea-Level ?
No full textCorrelation of Grassy Lake and Cedar Lake ambers using infrared spectroscopy, stable isotopes, and palaeoentomology
No full textThe Late Cretaceous Grassy Lake and Cedar Lake amber deposits of western Canada are among North America’s most famous amber-producing localities. Although it has been suggested for over a century that Cedar Lake amber from western Manitoba may be a secondary deposit having originated from strata in Alberta, this hypothesis has not been tested explicitly using geochemical fingerprinting coupled to comparative analyses of arthropod faunal content. Although there are many amber-containing horizons associated with Cretaceous coals throughout Alberta, most are thermally mature and brittle, thus lacking the resilience to survive long distance transport while preserving intact biotic inclusions. One of the few exceptions is the amber found in situ at Grassy Lake. We present a suite of new analyses from these and other Late Cretaceous ambers from western Canada, including stable isotopes (H and C), Fourier transform infrared (FTIR) spectra, and an updated faunal compendium for the Grassy and Cedar lakes arthropod assemblages. When combined with amber’s physical properties and stratigraphic constraints, the results of these analyses confirm that Cedar Lake amber is derived directly from the Grassy Lake amber deposit or an immediate correlative equivalent. This enables the palaeoenvironmental context of Grassy Lake amber to be extended to the Cedar Lake deposit, making possible a more inclusive survey of Cretaceous arthropod fauna
Chapter Eleven Biomarkers as Paleoceanographic Proxies
No full textIn palaeoceanography the term biomarker is used to name organic molecules found in sediments, initially produced by a variety of organisms either on land or in the aquatic environment. A key characteristic of biomarkers is that after their biosynthesis, and the death of the source organisms, they survive deposition to sediments in a recognizable form in terms of their original structure and sterical configuration (that is, spatial distribution of the atoms). They can thus be considered chemical fossils. The usefulness of organic components as palaeoproxies largely depends on their resilience to early degradation processes during sedimentation and after incorporation into the sediment. The most common biomarkers used as climate proxies belong to a few compound types, namely C37 alkenones and n-alkyl lipids. The key factors that make them suitable as proxies are that they are extremely common in sediments, their sources are identified, and their study provides information on key environmental variables. Biomarkers may be transported to sediments as part of the remains of the original organism (for example, leaf debris, marine snow), its digested remains (for example, faecal pellets), or adsorbed to mineral particles (that is, ballast minerals: silicate and carbonate biominerals, and dust), which eventually settle on the ocean bottom through gravity. The chapter describes the various approaches at distinct stages in their development and application
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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