1,720,995 research outputs found
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
Sedimentary record of Upper Triassic impact in the Lagonegro Basin, southern Italy: Insights from highly siderophile elements and Re-Os isotope stratigraphy across the Norian/Rhaetian boundary
Full text linkThe Norian and Rhaetian transition (Late Triassic) is characterized by a faunal turnover in major pelagic groups, such as radiolarians, conodonts, and ammonoids. Although catastrophic events such as emplacements of large igneous provinces and/or extraterrestrial impacts have been suggested to account for this biotic turnover, firm evidence based on geochemistry of sedimentary successions is still lacking. In order to assess environmental changes across the Norian/Rhaetian boundary (NRB), we report high–resolution stratigraphic variations for whole-rock major, trace, and highly siderophile element abundances, together with Re–Os isotope ratios for the Sasso di Castalda section in Lagonegro Basin, southern Italy. The section consists of a continuously exposed sequence of upper Norian (Sevatian) through the lower Rhaetian of a deep basinal deposits. Our data demonstrated that the upper Norian section records important events in stratigraphically ascending order: (1) a depositional environment moved below the Carbonate Compensation Depth, leading to the carbonate-biosilica transition associated with a slight depletion of elements favored in heavy minerals such as Zr, Hf, and Ti, (2) an input of Rochechouart impact components detected by platinum-group element anomaly, and (3) a transient change of redox state into low oxygen (dysoxic to suboxic) conditions marked by increases of V, U, and Re. This sequence of events suggests that the Rochechouart impact predates the major environmental changes resulting in faunal turnover at the NRB. Although their direct causal relationships are highly questionable given the small size of impactor and the interval between the impact horizon and the NRB, the possibility of triggering subsequent environmental and biotic collapses cannot be ruled out. This study provides the first identification of Rochechouart impact horizon in marine strata, which could be an important event marker for further studies on contemporaneous sections in the Lagonegro Basin and other localities
A dilute sodium hydroxide technique for radiolarian extraction from cherts
Full text linkRadiolarians have been used to determine geological ages and have contributed markedly to our understanding of Earth’s history. Hydrofluoric acid (HF) has traditionally been used to extract radiolarian fossils from siliceous deposits (i.e., radiolarian cherts), but this acid is strictly regulated because of environmental and human health concerns. Here we report on the successful extraction of radiolarians from cherts using a low-concentration NaOH solution (1 mol/L NaOH) as an alternative to HF. The degree of chert dissolution in NaOH is strongly temperature-dependent and is limited at < 80 °C. However, even a 1 mol/L NaOH solution is sufficient to dissolve chert at 100 °C. Our new NaOH method yields better-preserved radiolarian fossils compared with the conventional HF method. The 1 mol/L NaOH solution is less hazardous, easier to handle, and has fewer effects on the environment and human health than HF. Therefore, this method can be widely used for research and teaching purposes in studies of radiolarian fossils, even in institutions where HF cannot be used owing to chemical restrictions
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
A new method for extracting conodonts and radiolarians from chert with NaOH solution
Full text linkMicrofossils are important components of sedi- mentary rocks used for palaeontological, biostratigraphic, palaeoenvironmental and palaeoclimatic investigations. They are usually extracted from rocks using an acid solution, which might vary depending on the embedding rock lithology. Here we propose a new method using common NaOH (sodium hydroxide; soda) to digest cherts (micro- and cryptocrystalline quartz) instead of the standard technique based on HF (hydrofluoric acid). This new method allows the collection of undamaged specimens of different kinds of microfossils, such as conodonts, radiolarians, teeth and dermal scales, the miner- ology of which is still preserved (e.g. biogenic apatite in cono- donts). The use of soda is thus recommended, as it is less dangerous, less expensive, and it better preserves the extracted microfossils both in shape and mineralogy
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
Climax in Wrangellia LIP activity coincident with major Middle Carnian (Late Triassic) climate and biotic changes: Mercury isotope evidence from the Panthalassa pelagic domain
Full text linkThe Carnian Pluvial Episode (CPE, -233 Ma) was characterized by multiple negative carbon-isotope excursions, turnovers in marine and terrestrial biota, and a Tethys-wide humid climate accompanied by abundant terrigenous sediment and freshwater input into sedimentary basins. A general temporal coincidence between the CPE and the emplacement of the Wrangellia Large Igneous Province (Wrangellia LIP) has been well documented, however, it remains unclear whether fluctuations in the intensity of the LIP's activity could be linked to the biotic and climate changes at the CPE. We here present mercury (Hg) concentration and isotope ratio records from a pelagic deep-water succession (Section N-O, Inuyama, Japan) that encompasses the CPE interval. Data reveal concurrent peaks in the Hg concentrations and ratios of Hg to TOC and enrichment factors ThEF, AlEF, ZnEF, and NiEF implying that excess Hg loading in the sediments occurred, likely due to volcanic activity, prior to the CPE siliciclastic input. Furthermore, A199Hg values show a negative shift across the boundary between the Julian 1 and Julian 2, followed by a positive shift up to near-zero values at the Julian/Tuvalian transition. The near-zero A199Hg values at the Julian/Tuvalian boundary are associated with an increase in Hg and Cu loading, suggesting a peak of volcanogenic Hg and Cu input that may indicate a climax in the Wrangellia LIP activity. Most notably, the Julian/Tuvalian transition is where evidence of the most pronounced changes in carbonate platform evolution, biological turnover and climate change associated with the event has been highlighted. Our results therefore suggest that variations in the intensity of LIP volcanism may have played a major role in driving biotic and climate changes during the CPE. Our results provide a model for other mass extinction events associated with LIPs (e.g., the end-Permian) where low-intensity background volcanism was punctuated by high-intensity pulses, these latter being the real killers
Evolutionary Process from Mockina bidentata to Parvigondolella andrusovi: Evidence from the Pizzo Mondello Section, Sicily, Italy
Full text linkDuring their last phase of evolution, the pectiniform conodont elements manifested an evident trend of simplification and miniaturization. This phase started from the late Norian (Sevatian) in the Late Triassic and the evolutionary process of genus Mockina to Parvigondolella, in particular between Mockina bidentata and Parvigondolella andrusovi, is one of the most significant examples. Parvigondolella has been reported worldwide since it was first described in the early 1970s. However, it has recently been suggested that genus Parvigondolella is an ecostratigraphic morphotype of genus Mockina, and thus a phenotype controlled by the environmental conditions, and not an independent taxon. In the Pizzo Mondello Section (Sicily, Italy), transitional forms between M. bidentata and P. andrusovi have been found at different evolutionary stages. We have investigated the oceanic conditions at the time by using redox-sensitive elements (Mn, Fe, V, Cr, and Ni) and seawater temperatures from biogenetic δ18Ophos to understand the possible environmental influences on the phylogenetic evolution between Mockina and Parvigondolella. The geochemical and isotope analyses indicate that the redox condition and temperature were stable during the evolution of genus Parvigondolella in Pizzo Mondello, confirming that genus Parvigondolella is a real taxon and not a phenotype. A new conodont species named Parvigondolella ciarapicae n. sp. is described here for the first time
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