1,720,966 research outputs found
The first documented co-occurrence of conodonts and graptolites in Silurian (Telychian) black shales of the Prague Synform, Czech Republic, and its stratigraphical and palaeoecological significance
No full textThe Želkovice locality, located in the south-western part of the Prague Synform, is well-known for its exceptionally well-preserved graptolites in black shales. Despite being studied repeatedly by several authors for over 170 years, no record of conodonts has been found until now. Both conodonts and graptolites are significant biostratigraphic groups of Paleozoic fossils. However, papers about their co-occurrence are rare. Their occurrence is tied to distinct lithofacies, which makes direct biozonal correlation difficult. Their partial overlap sheds new light on ecological niches, resilience, and the palaeoecological conditions of the environment. Determined conodonts belong to cosmopolitan taxa with a long range, inhabiting the deeper, distal parts of the shelf or continental slope. A total of 10 conodont species were identified at the same locality, spanning the entire linnaei Biozone. The occurrence of the index species Distomodus staurognathoides, whose stratigraphic range overlaps with the locally used graptolite linnaei Biozone and the internationally used guerichii Biozone, is documented. This study also documents rare specimens
of pelagic fauna for the first time and discusses hypothetical parasitism and predation in conodonts and graptolites. This is the first study to describe the co-occurrence of both groups within the same lithology (black shale) and stratigraphic level, not only at the Želkovice site, but also elsewhere in the Silurian of the Prague Synform
Ontogeny of Ancyrodelloides carlsi (Boersma) and comments on its generic attribution (Conodonta, Lower Devonian)
Full text linkThe ontogeny of the Lochkovian conodont species Ancyrodelloides carlsi (Boersma) is demonstrated thanks to a rich population from Morocco. The studied sample includes elements at various growth stages from juvenile to gerontic. The data are confirmed by several elements in collections from several localities in the Carnic Alps (Italy and Austria). The absence of terraces at every stage of growth and the presence of a strong denticulated lateral process confirms the generic attribution of the species to genus Ancyrodelloides. Comments on the apparatus are provided. The geographical distribution of the species, limited to Europe and the Mediterranean region, challenges its stratigraphic value for long distance correlations
The Devonian/Carboniferous boundary in Sardinia (Italy)
No full textIn Sardinia (Italy) two sections, located in the southeastern part of the island, expose the Devonian/Carboniferous Boundary: the Monte Taccu Section and the Bruncu Bullai section. Both expose limestones from the middle Famennian to the lower Tournaisian Siphonodella jii Zone. The limestone sequence is interrupted by a thin level of shales representing the Hangenberg Event. Data on conodont biostratigraphy and magnetic susceptibility across the Devonian/Carboniferous
Boundary are here summarised and reviewed
Chrono-, litho- and conodont bio-stratigraphy of the Rauchkofel Boden Section (Upper Ordovician–Lower Devonian), Carnic Alps, Austria
Full text linkAn updated stratigraphy of the Rauchkofel Boden Section, a classical reference section for the
Carnic Alps that exposes rocks from the Katian (Upper Ordovician) to the Pragian (Lower Devonian) is here
presented, following latest developments in conodont taxonomy and biostratigraphy, as well as in chrono -
stratigraphy, and the recent introduction of a new lithostratigraphic outline of the Carnic Alps. The original
conodont collection of the ’70s and ʼ80s was restudied and complemented by a detailed resampling in order
to achieve a more precise conodont biostratigraphic assignment. Twenty-five conodont Zones are now documented.
The lithostratigraphy is precisely fixed to the new lithostratigraphic scheme of the Pre-Variscan sequence
by definition of seven distinct formations. Finally, the position of chronostratigraphic boundaries is
discussed
Bojen-Seelilien (Scyphocrinitidae, Echinodermata) in neu-datierten Schichten vom oberen Silur bis untersten Devon Südost-Marokkos [Buoy crinoids (Scyphocrinitidae, Echinodermata) in newly dated Upper Silurian to lowermost Devonian strata of SE Morocco]
No full textIn den Alaunschiefern des hohen Silurs – untersten Devons im Tafilalet-Gebiet von SE-Marokko sind mehrere Bänke
und linsenförmige Lagen aus Massen von oft sehr gut erhaltenen Scyphocrinoiden eingeschaltet. Diese zu der Zeit
weltweit verbreiteten großen Crinoiden hatten durch Umwandlung ihrer normalerweise als Verankerungsorgan dienenden
Wurzel in eine gekammerte Schwimmboje („Lobolith“) das Plankton-reiche Oberflächenwasser als neuen Lebensraum
gewonnen. Die lagigen Massenvorkommen entstanden wahrscheinlich durch gelegentliche Sturmwetter-Ereignisse,
bei denen viele Bojenwurzeln abgerissen wurden, so dass Kolonie-artige, wohl durch lange Algen miteinander
verbundene Ansammlungen dieser Tiere ihren Gesamt-Auftrieb verloren und in ein eutrophiertes H2S-reiches Milieu
am Meeresboden absanken, wo sie oft in sehr guter Erhaltung fossilisierten. Obwohl sich im oberen Silur mehrere Scyphocrinoiden-
Arten entwickelt hatten, bestehen die „Kolonien“ jeweils nur aus einer Art. Die Conodonten-stratigraphische
Untersuchung von drei Profilen in SE-Marokko zeigt, dass im oberen Silur zunächst nur Formen mit einem
bautechnisch ursprünglicheren Cirren-Lobolithen vorkommen (Scyphocrinites und Carolicrinus); im höheren Bereich der
Unteren detortus- und v. a. in der Oberen detortus-Conodonten-Zone kommen Lagen mit Scyphocrinoiden hinzu, die einen
deutlich verbesserten Platten-Lobolithen entwickelt hatten: Arten von Marhoumacrinus und/oder Camarocrinus, die
dann im untersten Devon (hesperius-Zone) als alleinige und letzte Vertreter dieser Crinoidengruppe nachzuweisen sind.Stratigraphical occurrence and biology of the large pelagic scyphocrinoids (with their biostratinomically always separated
buoy-like bulbous root, the lobolith) are investigated in three sections of the S–D boundary layers in the Tafilalet
region. These successions of Přídolí–lower Lochkovian alum shales with several scyphocrinoid beds with crowns, stems
and loboliths can be divided into four conodont zones. First scyphocrinoids appear in the eosteinhornensis s. l. Zone: species
of Scyphocrinites and Carolicrinus in separate beds, both exclusively being associated (and, hence, to be anatomically
combined) with the biotechnically relatively primitive type of buoy, the “cirrus lobolith“
The “Lochkovian-Pragian Event” re-assessed: New data from the low latitude shelf of peri-Gondwana
Full text linkIn the late Lochkovian a regression is documented in several areas of the world, followed by a transgression in the early Pragian. Connected with the eustatic variation, a minor extinction event occurred (“Lochkovian-Pragian Event”), affecting several fossil groups, a strong reduction of carbonate production and sedimentary facies changes. The Carnic Alps are a key area for studying this event, because Lower Devonian rocks are widely exposed, representing diverse sedimentary environments from shallow water to relatively deep shelf. Fourteen sections were measured along the Carnic Alps across the Lochkovian-Pragian boundary. In the shallower part of the basin, both the Polinik and the Seekopf formations span the boundary, but evident erosional surfaces are observable in the field at the Lochkovian-Pragian boundary. Above the unconformity, at places the so-called megaclast horizon is present in the Seekopf Formation. In intermediate settings the Rauchkofel Fm. is unconfomably followed by the Kellerwand Fm., and different parts of the upper Lochkovian and lower Pragian are missing in the various sections. In the deeper parts of the basin the transition from the La Valute Fm. to the Findenig Fm. is slightly diachronous from the latest Lochkovian to the earliest Pragian; however, conodonts and tentaculitids are rare in the marly boundary beds, preventing a precise chronostratigraphic calibration of these levels. At places, evidence of subaerial exposure at the formational boundary is documented. In general, the hiatus seems to be larger in the western part of the Carnic Alps, in correspondence with the shallower parts of the succession, suggesting a sea level drop in the late Lochkovian, followed by a transgression in the Pragian. Data from the Carnic Alps are compared with those of other regions of North Gondwana to demonstrate that the sealevel variation at the Lochkovian-Pragian boundary are of global importance
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
- …
