1,721,049 research outputs found
Volume calculation of Paleocene calcareous nannofossils
No full textDuring the past decades, volume calculation of extant calcareous nannoplankton has been performed in order to convert coccolith fluxes data into carbonate export productivity. The most useful and relative recent method to estimate the volume of coccoliths is described by Young & Ziveri (2000). Several studies on estimates of recent coccolithophore carbonate contribution have been published and this methodology has also been successfully applied to Mesozoic sediments (Tremolada & Young, 2002), thus providing a new promising proxy to be used in paleoceanographic reconstructions. Based on these fruitful practices, we have decided to test these methodologies on Paleocene sediments from several DSDP/ODP Sites. The study areas are located at different latitudes both in the Atlantic (401, 690, 1051, 1260 and 1263) and Pacific (ODP Site 1209) Oceans with the intention of giving a global perspective. We have investigated well-preserved deep-sea sediments in order to determine the average dimensions and calculate the volume of the most abundant Paleocene nannofossils, which include Coccolithus, Toweius, Sphenolithus, Fasciculithus, Discoaster and Zygrhablithus. For each taxon, we have measured at least 250 specimens to obtain accurate size estimates; furthermore, we have analyzed 30 specimens of each species to calculate shape constant (Ks), which, in turn, is used to obtain calcareous nannofossil volumes. This approach permits to evaluate the total amount of CaCO3 produced by coccoliths and could be used to provide an important tool for palaeoecological and biogeochemical interpretations. However, the present work represents the first attempt to investigate the significance of volume variation within Paleocene nannofloras
Late Paleocene to Early Eocene Magneto-Biostratigraphy from the Cicogna section (Belluno Basin, NE Italy): A record of continental weathering
Get PDFDuring the Late Paleocene-Early Eocene (̃60 Ma to 50 Ma), Earth's climate experienced a warming trend that culminated at the Early Eocene Climatic Optimum (EECO). The EECO was characterized by warm conditions at even extreme high latitudes, subdued latitudinal temperature gradients, and virtually nonexistent polar ice sheets. The early Paleogene long-term climate was punctuated by several short-lived hyperthermal events, the most prominent of which is the Paleocene Eocene Thermal Maximum (PETM). Here we present paleomagnetic and calcareous nannofossil data from the Tethyan marine Cicogna section (Belluno Basin, NE Italy). The paleomagnetic results, integrated with calcareous nannofossil biostratigraphy, indicate that the Cicogna section extends from Chron C25r to Chron C23r spanning the NP7/NP8-NP12 nannofossil Zones with a relatively constant sediment accumulation rate of ̃18 m/My. Rock-magnetic data show sediment enrichment in hematite-maghemite respect to magnetite generally across the PETM and from ̃54 Ma up to the section top. We observed a correlation between rock-magnetic properties and global climate as revealed by a standard benthic oxygen isotope record from the literature. Our interpretation is that the warm and humid conditions typical of the PETM and the EECO enhanced continental weathering with the consequent production, transport, and sedimentation of more oxidized iron oxide phases (e.g. hematite-maghemite) relative to less oxidized phases (e.g., magnetite). Our temporal coupling between oxidation state of sedimentary magnetic phases and global climate therefore demonstrates the existence in the Paleocene-Eocene of the silicate weathering negative feedback mechanism for the long-term stabilization of the Earth's surfaces temperature as proposed by various authors
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
Late Paleocene to Early Eocene magneto-biostratigraphy of the Cicogna section (Belluno Basin, NE Italy)
No full textDuring the Late Paleocene-Early Eocene (~60 Ma to 50 Ma), Earth's climate experienced a warming trend that culminated at the Early Eocene Climatic Optimum (EECO). The EECO was characterized by warm conditions at even extreme high latitudes, subdued latitudinal temperature gradients, and virtually nonexistent polar ice sheets. A persistent cooling trend occurred during the Middle and Late Eocene and eventually drove the Earth climate into the current glacial mode. The early Paleogene long-term climate was punctuated by several short-lived hyperthermal events, the most prominent of which is the Paleocene Eocene Thermal Maximum (PETM). Here we present paleomagnetic and calcareous nannofossil data from the Tethyan marine Cicogna section (Belluno Basin, NE Italy). The paleomagnetic results, integrated with calcareous nannofossil biostratigraphy, indicate that the Cicogna section extends from Chron C25r to Chron C23r spanning the NP7/NP8-NP12 nannofossil Zones with a relatively constant sediment accumulation rate of ~18 m/My. To extend the magnetic property characterization of the Belluno Basin sediments in the Early and Middle Eocene, we integrated the Cicogna magnetic analysis results with data from the neighboring Possagno section. Rock-magnetic data show a gradual relative increase in pigmentary (fine-grained) hematite within the sediments that peaked at ~49-50 Ma. This datum is interpreted as related to enhanced continental weathering processes under EECO warm climate conditions. The Middle-Late Eocene cooling trend following the EECO was than characterized by a gradual relative decrease of the fine-grained hematite content of the sediments toward pre-warming values. Our findings contribute to the understanding of the coupling between long-term Earth's climate and silicate weathering processes during the Eocene
An expanded Cretaceous−Tertiary transition in a pelagic setting of the Southern Alps (central-western Tethys)
Get PDFThe central part of the Piave River valley in the Venetian pre-Alps of NE Italy exposes an expanded and continuous marine sediment
succession that encompasses the Paleocene series and the Paleocene to Eocene transition.
The Paleocene through lower most Eocene succession is >100 m thick and was deposited at middle to lower bathyal depths in a
hemipelagic, near-continental setting in the central western Tethys. In the Forada section, the Paleocene succession of limestone-marlm couplets is sharply interrupted by an ~3.30-m-thick unit of clays and marls (clay marlunit). The very base of this unit represents the biostratigraphic Paleocene-Eocene boundary,
and the entire unit coincides with the main carbon isotopeexcursion of the Paleocene-Eocene thermal maximum event. Concentrations of hematite and biogenic carbonate, δ13C
measurements, and abundance of radiolarians, all oscillate in a cyclical fashion and are interpreted to represent precession cycles. The main excursion interval spans fi ve complete cycles, that is, 105 ± 10 k.y. The overlying carbonisotope recovery interval, which is composed of six distinct limestone-marl couplets, is interpreted to represent six precessional cycles with a duration of 126 ± 12 k.y. The entire carbon isotope excursion interval in Forada has a total duration of ~231 ± 22 k.y., which
is 5%–10% longer than previous estimates derived from open ocean sites (210–220 k.y.).
Geochemical proxies for redox conditions indicate oxygenated conditions before, during, and after the carbon isotope excursion event.
The Forada section exhibits a nonstepped sharp decrease in δ13C (−2.35‰) at the base of the clay marl unit. The hemipelagic, near-continental depositional setting of Forada and the sharply elevated sedimentation rates throughout the clay marl unit argue for continuous rather than interrupted deposition and show that the initial nonstepped carbon isotope shift was not caused by a hiatus. A single sample at the base of the unit lacks biogenic carbonate.
Preservation of carbonate thereafter improves progressively up-section in the clay marl unit, which is consistent with a prodigiously abrupt and rapid acidifi cation of the oceans followed
by a slower, successive deepening of the carbonate compensation depth. Increased sedimentation rates through the clay marl unit
(approximately the main interval of the carbon isotope excursion) are consistent with an intensifi ed hydrological cycle driven by supergreenhouse conditions and enhanced weathering and transport of terrigenous material to this near-continental, hemipelagic environment
in the central western Tethys.
The sharp transition in lithology from the
clay marl unit to the overlying limestonemarl
couplets in the recovery interval and
the coincident shift toward heavier δ13C values
suggest that the silicate pump and continental
weathering, the cause of the enhanced
terrigenous fl ux to Forada, stopped abruptly.
This implies that the source of the light CO2
ceased to be added to the ocean-atmosphere
system at the top of the clay marl unit
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