1,720,976 research outputs found
Late Triassic biostratigraphic constraints in the Imagna Valley (western Bergamasc Alps, Italy)
No full text
THE HETTANGIAN SHALLOW WATER CARBONATES AFTER THE TRIASSIC/JURASSIC BIOCALCIFICATION CRISIS: THE ALBENZA FORMATION IN THE WESTERN SOUTHERN ALPS
No full textThis study investigates the stratigraphic and sedimentologic setting of an early Hettangian carbonate platform in the Lombardy Basin, taking into account the Triassic-Jurassic (Tr-J) post-crisis evolution and the geodynamic setting related to the beginning of the Early Jurassic rifting. The historical name of this platform ("Conchodon Dolomite"), not adequate for the absence of Conchodon and for the mainly calcareous lithology, has been replaced with Albenza Formation. The depositional model of this carbonate platform unit is coherent with a leeward Great Bahama Bank-type environment, without any reefs facing deep water environments. The unusual abundance of ooids and marine cements, in the basal progradational ramp-type margins, reflects temporal variation in the saturation state of seawater after the Tr-J crisis, possibly due to marine calcified cyanobacteria blossom. The absence of biotically induced margins related to the (biocalcification) Tr-J crisis and the concomitant tectonic fragmentation, with different subsidence rates of the Tethyan passive margin, conditioned the drowning and the eastward retrogradation of the Albenza platform
Anomalies in global carbon cycling and extinction at the Triassic/Jurassic boundary : evidence from a marine C-isotope record
No full textThis study investigates whether the end-Triassic biotic crisis was coupled with a perturbation of the marine C-isotope budget. The marine C-isotope signature serves as a proxy of the marine carbon reservoir and ultimately of the global C cycle. A
continuous shallow water marine limestone succession from the Western Southern Alps (Bergamasc Alps, northern Italy) provides information on the end-Triassic biotic crisis and on the evolution of the marine carbon reservoir across the Triassic/
Jurassic (T/J) boundary. The established carbonate C-isotope curve is marked by a negative C-isotope pulse coinciding with the disappearance of the end-Triassic benthic faunal assemblage and a widespread Rhaetian carbonate platform drowning event.
The negative spike is followed by a positive C-isotope excursion starting at the palynological T/J transition. The negative Cisotope pulse may have resulted from the sudden release of gas hydrates. The positive isotope excursion records a global change in organic carbon burial rates, probably in response to elevated atmospheric CO2 levels at a time of massive volcanic activity in
the Central Atlantic Magmatic Province. High CO2 levels were responsible for the end-Triassic biocalcification crisis, carbonate platform collapse, and, possibly, the sudden release of methane from gas hydrate
Stratigraphic evolution of the Triassic–Jurassic succession in the Western Southern Alps (Italy) : the record of the two-stage rifting on the distal passive margin of Adria
Full text linkThe Triassic-Lower Jurassic succession of the Southern Alps is characterized by rapid thickness changes, from an average of about 5000m east of Lago Maggiore to about 500m in the Western Southern Alps. The stratigraphy reflects the Triassic evolution of the Tethyan Gulf and the Early Jurassic rifting responsible for the Middle Jurassic break-up of Adria from Europe. The succession of the Western Southern Alps starts with Lower Permian volcanics directly covered by Anisian sandstones. The top of the overlying Ladinian dolostones (300m) records subaerial exposure and karstification. Locally (Gozzano), Upper Sinemurian sediments cover the Permian volcanics, documenting pre-Sinemurian erosion. New biostratigraphic data indicate a latest Pliensbachian-Toarcian age for the Jurassic synrift deposits that unconformably cover Ladinian or Sinemurian sediments. Therefore, in the Western Southern Alps, the major rifting stage that directly evolved into the opening of the Penninic Ocean began in the latest Pliensbachian-Toarcian. New data allowed us to refine the evolution of the two previously recognized Jurassic extensional events in the Southern Alps. The youngest extensional event (Western Southern Alps) occurred as tectonic activity decreased in the Lombardy Basin. During the Sinemurian the Gozzano high represents the western shoulder of a rift basin located to the east (Lombardy). This evolution documents a transition from diffuse early rifting (Late Hettangian-Sinemurian), controlled by older discontinuities, to rifting focused along a rift valley close to the Pliensbachian-Toarcian boundary. This younger rift bridges the gap between the Hettangian-Sinemurian diffuse rifting and the Callovian-Bathonian break-up. The late Pliensbachian-Toarcian rift, which eventually lead to continental break-up, is interpreted as the major extensional episode in the evolution of the passive margin of Adria. The transition from diffuse to focused extension in the Southern Alps is comparable to the evolution of the Central Austroalpine during the Early Jurassic and of the Central and Northern Atlantic margins
Palaeoceanographic model for the Early Toarcian black shales in the Maglio sections (Southern Alps, Italy) : palynological, calcareous nannofossil and stable-isotope analyses
No full textThe early Toarcian Oceanic Anoxic Event (T-OAE, 183 Ma, Early Jurassic) represents a period of widespread to global deposition of organic-rich sediments in a variety of marine settings. It is one of the most dramatic palaeoceanographic episodes in Earth history leading to (extremely) high rates of organic-carbon burial and a general
decrease in calcium carbonate deposition. The T-OAE is associated with large global carbon-isotope anomalies in carbonate and/or organic matter, caused by a major perturbation of the global carbon cycle. An overall positive carbon-isotope excursion (dated as tenuicostatum to falciferum ammonite zones) is over-printed by a short-lived negative isotopic shift (exaratum ammonite sub-zone) in marine and terrestrial reservoirs.
The negative anomaly has been interpreted to indicate raised atmospheric CO2 caused by oxidation of isotopically light methane released either from marine gas hydrates or magma-intruded coal-bearing strata.
Although the chemical changes that occurred in the ocean/atmosphere system during the T-OAE are well described, the adaptation of planktonic communities remains to be fully understood, particularly in the low-latitude Tethyan region, where carbonatefree, stratigraphically condensed and incomplete successions are common. This study
is focused on a stratigraphically expanded, complete and clay-rich pelagic section (Maglio) located in the Southern Alps (Northern Italy). Biostratigraphic investigations and quantitative analysis based on palynomorphs and calcareous nannofossils were undertaken, using the relative abundance of single species for palaeoecological
and palaeoceanographic reconstructions. Carbon- and oxygen-isotope stratigraphy on the same samples has aided correlation with other well-characterized coeval sections.
These isotope curves show relatively low 13C and 18O values, typical of the negative
excursion characteristic of the interval, as well as some anomalously negative‘spikes’ attributed to diagenesis. Based on the obtained dataset, a palaeoceanographic model, characterized by three
distinctive phases, is proposed. In this model, the black shales deposited during the
T-OAE are assumed to have been deposited under warm and humid conditions, with relatively high wind speeds, precipitation rates and continental runoff, related to an accelerated hydrological cycle (increase of sporomophs and meso-eutrophic calcareous nannofossils - Phases 1–3). This palaeoenvironmental change could not only have
forced an increase in organic productivity due to accelerated nutrient flux to the oceans
but also accentuated thermohaline stratification, further aiding development of anoxic conditions in the bottom waters: both factors (enhanced productivity, enhanced preservation) would have favoured accumulation of organic matter. In this model, a dinoflagellate cyst event (“Luehndea spike” - Phase 2) indicates a relative drop in temperature and/or rise in surface-water salinity with respect to the other phases
Stratigraphy and palaeoenvironmental analysis of the Triassic-Jurassic transition in the western Southern alps (Northern Italy)
No full textHigh resolution stratigraphic studies were carried out on the Rhaetian–Hettangian succession of the Bergamasc Alps (western
Southern Alps, Italy) in order to characterise the stratigraphic and palaeoenvironmental evolution of the Lombardian succession
across the Triassic–Jurassic (T–J) boundary. The T–J boundary in the Bergamasc Alps is sandwiched between the Rhaetian
carbonate ramp succession of the Zu Limestone Formation and the Malanotte Formation (a new lithostratigraphic unit introduced in
this paper), deposited during relative sea-level rise in the earliest Hettangian. The Zu Limestone is organised into subtidal mixed shale-carbonate asymmetric cycles documenting the regional evolution from a distal to a proximal depositional environment of an articulated homoclinal carbonate ramp. The Malanotte Formation lacks cyclicity and shows thin bedding and a dominant micritic facies, documenting the subtidal evolution of a relatively homogenous outer carbonate ramp environment.The microfloral associations record a gradual evolutionary change at the T–J boundary, whereas the biocalcifying communities appear to be severely affected by the end-Triassic biotic crisis
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
- …
