1,721,027 research outputs found
Cenomanian-Turonian boundary diachroneity unraveled by highly resolved carbon-isotope cyclostratigraphy from the Paris Basin Chalk
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Coupling between Grand cycles and Events in Earth’s climate during the past 115 million years
No full textInternational audienceGeological sediment archives document a rich periodic series of astronomically driven climate, but record also abrupt, severe climatic changes called events, the multi-Myr boundary conditions of which have generally been ascribed to acyclic processes from Earth’s interior dynamics. These events have rarely been considered together within extended time series for potential correlation with long-term (multi-million year, Myr) cycling. Here I show a coupling between events and multi-Myr cycles in a temperature and ice-volume climatic proxy of the geological past 115 Myr. I use Cenozoic through middle Cretaceous climatic variations, as recorded in benthic foraminifera δ18O, to highlight prominent ~9 and ~36 Myr cyclicities. These cyclicities were previously attributed either to astronomical or tectonic variations. In particular, I point out that most of the well-known events during the past 115 Myr geological interval occur during extremes in the ~9 and ~36 Myr cycling. One exception is the early Cenozoic hyperthermal events including the salient Paleocene-Eocene Thermal Maximum (~56 Ma), which do not match extremes in long-period cyclicities, but to inflection point of these cycles. Specific focus on climatic events, as inferred from δ18O proxy, suggest that some “events”, marked by gradual trends within the ~9 and ~36 Myr cycle extremes, would principally be paced by long-term cycling, while “events”, recorded as abrupt δ18O changes nearby cycle extremes, would be rather induced by acyclic processes. The connection between cyclic and acyclic processes, as triggers or feedbacks, is very likely. Such link between cycling and events in Earth’s past climate provides insight into celestial dynamics governing perturbations in Earth’s surface systems, but also the potential connection between external and Earth’s interior processes
A ~9myr cycle in Cenozoic ?13C record and long-term orbital eccentricity modulation: Is there a link?
No full textThe ~ 65-myr-long Cenozoic carbon isotope record (?13C) of Zachos et al. (2001, 2008) documents a strong long-term cycle with a mean pseudoperiodicity close to ~ 9 myr. This cyclicity modulates the ~ 2.4 myr eccentricity cycle amplitude, hinting at a possible link between long-term astronomical and geological variations. Some phase shifts between ~ 9-myr ?13C and astronomical cycles suggest that additional processes (e.g., tectonics) contribute to these long-term carbon-cycle variations.The strong response of ?13C to long-term eccentricity periods (~ 9 myr, ~ 2.4 myr, ~ 400 kyr) supports the hypothesis that the long time-residence of carbon in the oceans amplifies lower frequency or dampens higher frequency orbital variations. Additionally, the strong expression of low-amplitude ~ 9 myr eccentricity cycle in the ?13C record could be explained by energy-transfer process from higher to lower frequency cycles, and all eccentricity components modulate the carrier climatic precession cycles.Finally, the Paleocene–Eocene Thermal Maximum (PETM, 55.9 Ma) event, which corresponds to a pronounced ?13C negative excursion, is situated within a strong decrease in the most prominent ~ 9 myr ?13C cycle, hinting at a link between accelerated rates in ?13C variations and the PETM. This specific ~ 9 myr ?13C cycle seems to be amplified by non-orbital mechanisms in atmosphere–continent–ocean system, such as previously suggested methane release from gas hydrate and volcanism
Cyclostratigraphie des séries sédimentaires du Jurassique supérieur (Sud-Est de la France, Nord de la Tunisie) (contrôle astro-climatique, implications géochronologiques et séquentielles)
No full textUne étude cyclostratigraphique à haute résolution a été entreprise, en utilisant les variations de la susceptibilité magnétique (SM), sur trois coupes marneuses oxfordiennes et deux coupes d alternances marno-calcaires kimméridgiennes du Bassin du Sud-Est de la France. Les séries marneuses oxfordiennes enregistrent avec les plus fortes amplitudes de SM, les cycles d excentricité à 100 et 405 ka. Les séries d alternances kimméridgiennes détectent plutôt préférentiellement les cycles de précession. Les durées estimées des zones d ammonites sont très proches de celles de l échelle des temps géologiques GTS2004 pour le Kimméridgien inférieur, mais notablement différentes pour l Oxfordien inférieur et moyen. Comparés aux séquences eustatiques de 3ème ordre de la charte globale de référence, les cycles d excentricité à 405 ka semblent contrôler les variations du niveau marin relatif au moins durant le Kimméridgien inférieur et l Oxfordien inférieur et moyen dans le Bassin du Sud-Est.PARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF
Eocene-Oligocene continental sediment natural gamma radiation data of the CDB1 drill-core (Rennes Basin, France)
No full textThe natural gamma radiation (NGR) data were acquired each 10 cm (see details below) on fluvio-lacustrine and palustrine sediment materials, from the continental CDB1 drill-core located in the Rennes Basin (Chartres de Bretagne, France, geographic coordinates: 48.04412074N; 1.71899076W, Elevation: +37m NGF, Nivellement Général de France). The studied geological time interval covers the Eocene-Oligocene transition interval, roughly from 31 to 38.5 Ma.
NGR measurements were conducted by the Semm Logging company during the drilling campaign of the CINERGY project (CDB1 borehole) during summer 2010, under the supervision of BRGM (Bureau de Recherches Géologiques et Minières, France), on behalf the contracting authority of Chartres-de Bretagne. The main objective of the CINERGY project was to explore the Cenozoic cover of the Armorican shield preserved in a small strike-slip basin. The CINERGY Project was funded by the BRGM, the AELB (Agence de l'Eau Loire-Bretagne) and the ADEME (Agence de l'Environnement et de la Maitrise de l'Energie) French agencies.
The NGR probe used during the CDB1 well logging consists of a scintillation detector (sodium iodide crystal coupled to a photo-multiplication tube), which converts gamma rays into electric pulses. The measured values are expressed in API (American Petroleum Institute) unit. This unit was calculated using a linear interpolation of raw data expressed in pulses per second (pps) according to a calibration set with a very stable source, the radioactivity of which is known in API unit. Because disintegration is a random phenomenon, raw measurements taken every 2 cm are integrated over a 25 cm long window and restored at a 10 cm step, which is consistent both with the crystal size and the average dip of the strata, nearly 15 degrees
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
Comment on "Chronology of the Early Toarcian environmental crisis in the Lorraine Sub-Basin (NE Paris Baso,)" by W. Ruebsam, P. Münzberger,and L. Schwark [Earth and Planetary Science Letters 404 (2014) 273–282]
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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
Author Correction: A Jurassic record encodes an analogous Dansgaard-Oeschger climate periodicity
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