1,721,207 research outputs found
Correlation between the Warepan/Otapirian and the Norian/Rhaetian stage boundary: implications of a global negative δ13Corg perturbation
No full textThe Norian/Rhaetian boundary interval (Late Triassic) is characterised by significant biotic turnover and severe climatic changes. However, this boundary still awaits formal definition. We have investigated the δ13Corg record within a well-preserved marine sequence exposed in the Kiritehere section, North Island, New Zealand. This section was located at higher latitudes (above 60°S) during the Triassic, and is considered the best exposed section representative of the New Zealand Warepan/Otapirian stage boundary. This is a regional boundary pertaining to the Zealandia region of Gondwana; it is described in the New Zealand Geological Timescale (NZGT) and it has been recognised as being correlative with the Norian/Rhaetian boundary. Using an integrated chemo- and biostratigraphic approach, we have identified a negative δ13Corg shift close to the disappearance of the standard-sized monotids (fossil bivalves) in the Kiritehere section. We interpret this negative shift to be the same negative δ13Corg shift that has been proposed to define the base of the Rhaetian. However, the position of the negative δ13Corg shift in the Kiritehere section is ca. 6.40 m below the accepted position of the Warepan/Otapirian boundary, based on biostratigraphy. This δ13Corg isotopic shift, best thought of as a chemostratigraphic event, is regarded here as a global phenomenon
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
Middle triassic ammonoid fauna from the recoaro and tretto areas (NE Italy) and its stratigraphic and paleobiogeographic evidence
No full textBetween the mid 19th and the beginning of the 20th centuries, several Austrian and German geologists such as Beyrich, Mojsisovics and Tornquist, studied the geology of the Recoaro area (NE Italy). They described important ammonoid faunas, the majority being collected from a stratigraphic unit known as the Nodosus Formation.
Among these faunas are problematic species that have been the focus of long discussion both from a biostratigraphic and taxonomic point of view. Unfortunately, most of the historical material has been either destroyed or lost, and recent studies in the field provided only a few scarce specimens thus making taxonomic revision difficult. One of the unresolved issues is related to the possible occurrence of the ceratitids peculiar to the Upper Muschelkalk of the Central Europa (Germanic) Basin and the Sephardic Triassic province among the Alpine ammonoids. An unexpected discovery of an old ammonoid collection stored at the Museo Geologico e Paleontologico of Padova University (MGP-PD) permitted confirmation of the presence of a distinctive ammonoid species Alloceratites tornquisti (Philippi) within the Triassic Recoaro domain. Two other species of Alloceratites have also been found in the Val Gola section near Trento. These occurrences are significant taxonomically, biostratigraphically and in relation to Middle Triassic sequence stratigraphy
Conodont and radiolarian biostratigraphic age constraints on Carnian (Upper Triassic) chert-hosted stratiform manganese deposits from Panthalassa: Formation of deep-sea mineral resources during the Carnian pluvial episode
No full textNumerous stratiform manganese deposits occur in the Permian to Jurassic bedded chert successions of the Jurassic accretionary complexes of the Chichibu, Mino–Tamba, and North Kitakami belts in Japan. These accretionary complexes consist of deep-sea sediments accumulated in a pelagic, open-ocean setting within the Panthalassa Ocean. Although the depositional ages and processes of the Permian and Jurassic manganese deposits in these accretionary complexes have been studied, the Triassic bedded chert-hosted stratiform manganese deposits are poorly understood. We investigated the occurrence and stratigraphic distribution of Triassic stratiform manganese deposits in Japan, constraining their ages by means of integrated conodont–radiolarian biostratigraphy. On the basis of the conodont and radiolarian biostratigraphies, the depositional age of the Triassic manganese deposits was constrained to the latest Julian to earliest Tuvalian (mid-Carnian). This age indicates that the formation of the Triassic manganese deposits occurred contemporaneously with the last eruptive phase of the Wrangellia Large Igneous Province (LIP) volcanism and subsequent changes in the deep-sea redox conditions in the Panthalassa Ocean during the Carnian pluvial episode (CPE). Therefore, these manganese deposits may have been formed with the hydrothermal activity associated with the eruption of the Wrangellia LIP and/or the subsequent changes in marine redox conditions in the CPE
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
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