940 research outputs found
The valanginian weissert oceanic anoxic event recorded in central-Eastern Sardinia (Italy)
No full textInvestigations on the S’Ozzastru section from the northern part of the Mt Albo area (central-eastern
Sardinia, Italy) for integrated litho- bio- and chemostratigraphy allowed the identification of the Valanginian Weissert
Oceanic Anoxic Event (OAE), testified by a positive carbon isotope excursion (CIE). The section, which represents
the deepest-water succession of the Valanginian in Sardinia, is composed of the Schiriddè Limestone followed by
the Siniscola Marl, both proposed as new lithostratigraphic units. The presence among the ammonites of Busnardoites
campylotoxus allows the attribution of the Schiriddè Limestone to the upper Lower Valanginian Inostranzewi Zone of
Reboulet et al. 2014. Further characterization of this unit was not possible since it is barren/almost barren of nannofossils.
The Siniscola Marl can be ascribed to the lower Upper Valanginian on the basis of the ammonite fauna indicating
the Verrucosum Zone, and of the nannofossil content suggesting the Zone NK3. The carbon isotope record in
the Siniscola Marl is characterized by a positive excursion with values up to 2.98 ‰. In the nannofossil assemblages,
nannoconids are not particularly abundant and are found, among others, together with C. oblongata, D. lehmanii, and
pentaliths. The scarcity of nannoconids is regarded as a biostratigraphic support for the identification of the Weissert
OAE, as it possibly reflects the “nannoconid decline” interval which characterizes this event. The end of the Weissert
OAE CIE is not recorded probably because of suppression of the upper part of the succession for tectonic causes
Palaeoenvironment and palaeoecology before and at the onset of Oceanic Anoxic Event (OAE)1a: Reconstructions from Central Tethyan archives
No full textIn this study, a new C-isotope stratigraphy combined with a revised litho-and biostratigraphy of Barremian-Aptian platform carbonates from the central-southern Apennines (Italy) is presented. The Santa Maria (Abruzzi Region) and the Monte Faito (Campania Region) sections were investigated in order to trace platform evolution during a time of major C-cycle perturbation before and during Oceanic Anoxic Event (OAE)1a. These successions are correlated at a regional scale with the Monte Raggeto reference section (Campania) where the Selli Level Equivalent (SLE) and the Magnetic Polarity Chron CM0r were recognised in earlier studies. Significant biotic and environmental changes are documented within the Late Barremian-Early Aptian interval; in particular, the Palorbitolina lenticularis-Lithocodium-Bacinella association followed by dark-brown microbial sediments reflect considerable ecological stress upon the oligotrophic carbonate platform community (mesotrophic or even eutrophic conditions) which precedes the onset of SLE by at least 1.2 myr. Moreover, this integrated approach has resulted in an improved age control which offers the opportunity to correlate the Apenninic sections with a succession from the French Urgonian platform (Cluses section) and with pelagic records from the Italian Umbria-Marche (Gorgo a Cerbara) and Belluno (Cismon Apticore) Basins. Pelagic biozonations and magnetostratigraphy have been projected into carbonate platform sequences. A prevailing eustatic origin has been attributed to some of the lower-frequency transgressive-regressive cycles (T/RFTs) that reflect third order sea-level oscillations. The new correlations indicate that comparable biotic and environmental changes, documented around the Tethys, are not always synchronous. The type of response of biota to C-cycle perturbations before and during OAE1a depends upon palaeolatitude, palaeogeography, palaeobathymetry and regional climate patterns
Evolution of central Tethyan carbonate platforms before and at the onset of Oceanic Anoxic Event (OAE)1a: timing of biotic and environmental changes
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Mesozoic climates and oceans – a tribute to Hugh Jenkyns and Helmut Weissert
No full textThis is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.The study of past greenhouse climate intervals in Earth history, such as the Mesozoic, is an important, relevant and dynamic area of research for many sedimentary geologists, geochemists, palaeontologists and climate modellers. The Mesozoic sedimentary record provides key insights into the mechanics of how the Earth system works under warmer conditions, providing examples of natural climate change and perturbations to ocean chemistry, including anoxia, that are of societal relevance for understanding and contextualizing ongoing and future environmental problems. Furthermore, the deposition of widespread organic-carbon-rich sediments (‘black shales’) during the Mesozoic means that this is an era of considerable economic interest. In July 2015, an international group of geoscientists attended a workshop in Ascona, Switzerland, to discuss all aspects of the Mesozoic world and to celebrate the four-decade-long contributions made by Hugh Jenkyns (University of Oxford) and Helmut Weissert (ETH Zürich) to our understanding of this fascinating era in Earth history. This volume of Sedimentology arose from that meeting and contains papers inspired by (and co-authored by!) Hugh and Helmi. Here, a brief introduction to the volume is provided that reviews aspects of Hugh and Helmi's major achievements; contextualizes the papers of the Thematic Issue; and discusses some of the outstanding questions and areas for future research
A revision of stratigraphic framework of the Apenninic carbonate platform successions (central-southern Italy) by comparison with other Tethyan shallow to deep marine sections.
No full textMesozoic climates and oceans – a tribute to Hugh Jenkyns and Helmut Weissert
No full textThe study of past greenhouse climate intervals in Earth history, such as the Mesozoic, is an important, relevant and dynamic area of research for many sedimentary geologists, geochemists, palaeontologists and climate modellers. The Mesozoic sedimentary record provides key insights into the mechanics of how the Earth system works under warmer conditions, providing examples of natural climate change and perturbations to ocean chemistry, including anoxia, that are of societal relevance for understanding and contextualizing ongoing and future environmental problems. Furthermore, the deposition of widespread organic-carbon-rich sediments (‘black shales’) during the Mesozoic means that this is an era of considerable economic interest. In July 2015, an international group of geoscientists attended a workshop in Ascona, Switzerland, to discuss all aspects of the Mesozoic world and to celebrate the four-decade-long contributions made by Hugh Jenkyns (University of Oxford) and Helmut Weissert (ETH Zürich) to our understanding of this fascinating era in Earth history. This volume of Sedimentology arose from that meeting and contains papers inspired by (and co-authored by!) Hugh and Helmi. Here, a brief introduction to the volume is provided that reviews aspects of Hugh and Helmi's major achievements; contextualizes the papers of the Thematic Issue; and discusses some of the outstanding questions and areas for future research
Change from rimmed to ramp platform forced by regional and global events in the Cretaceous of the Friuli-Adriatic Platform (Southern Alps, Italy)
No full textCarbonate platforms are sedimentary archives recording the evolution of the global carbon cycle. Their stratigraphic architecture depends on the regional tectonics, controlling subsidence rates and geome- tries, as well as the paleoceanography and evolutionary trends, controlling the different organisms thriving at their margins, such as frame-building corals or mound-building microbes. We present an integrated bio- and chemostratigraphic study of the Aptian to Santonian interval of a base-of-slope section located in the Southern Alps of northeastern Italy that we correlate with the classic section representing the Friuli-Adriatic Carbonate Platform, one of the largest isolated platforms of the low latitude Tethys. We show the effects of the end of the passive-margin stage and the interaction between foreland flexuring due to the growing Alps, to which the study area represented the retroforeland, and the approaching prowedge of the Dinarides. The Friuli-Adriatic platform margin shows an abrupt change from reef rimmed to ramp, where abundant microbial mounds provided the habitat for the rudists to thrive. This change occurred around the late Albian and likely correlates with the Oceanic Anoxic Event (OAE) 1d. The previous OAE's did not change the structure of this platform, whose margins were mostly rigid and colonized by corals and calcareous sponges. Late Albian was a time of important changes in paleoceanography in Tethys and North Atlantic Oceans. We propose that the paleooceanographic changes related to the OAE- 1d had more profound impacts on the Friuli-Adriatic Platform than the previous Cretaceous OAE's since they co-occurred with the tectonic transition from passive margin to foreland ramp. The increased subsidence rates, in conjuction with the important late Albian paleo- ceanographic changes, created favourable conditions for a dramatic change in the platform margin physiography and ecology
From Helmut Jürgensen’s former students: The game of informatics
No full textPersonal reflections are given on being students of Helmut Jürgensen. Then, we attempt
to address his hypothesis that informatics follows trend-like behaviours through the
use of a content analysis of university job advertisements, and then via simulation
techniques from the area of quantitative economics
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