1,721,218 research outputs found
Chronology of Cenozoic Antartic glacial history from circum-Antartic marine sedimentary records
No full textThe present research represents an integrated magnetostratigraphic and environmental magnetic study of Cenozoic sediments from selected circum-Antarctic drill cores. The studied cores were selected to obtain a more complete picture of glacial history that can only be obtained by linking ice-proximal records from the continental shelf to the deep-sea record through key drill sites from the Antarctic margin and other coeval sequences from the Southern Ocean. These locations include: (1) a Cape Roberts Project drill-hole from the Ross Sea, other sedimentary sequences from the Southern Ocean drilled in association with the Ocean Drilling Program (ODP), including (2) holes 689B, 689D, 690B and 690C (ODP Leg 113) from Maud Rise, Weddell Sea, and (3) a transect of two sites drilled during ODP Leg 188 across the Prydz Bay continental shelf (Site 1166) and rise (Site 1165) in the Indian Ocean sector of the Antarctic margin. The results presented in this thesis provide an improved view of the timing and extent of events associated with the onset and subsequent history of Antarctic glaciation. In addition to these findings, they provide further evidence for an external forcing mechanism driving the dynamics of the early Oligocene East Antarctic Ice Sheet during its initial development. Finally, beside these results, paleomagnetic results from ODP Site 1165 (Prydz Bay, Antarctica), ODP Site 883 (North Pacific Ocean), ODP Site 1124 (Southwest Pacific Ocean) and ODP Site 998 (Caribbean Sea), provide evidence that dissolution of magnetite is a common feature in sediments with elevated porewater silica concentrations (e.g. in the Southern Ocean). This observation has important implications for paleomagnetic investigations of siliceous sedimentary environments.</p
Integrated bio-magnetostratigraphy of ODP Site 709 (equatorial Indian Ocean).
No full textOver the last decade, calcareous nannofossil biostratigraphy of the lower Eocene-Oligocene sediments has shown
great potential, through identification of several new nannofossil species and bioevents (e.g. Fornaciari et al., 2010;
Bown and Dunkley Jones, 2012; Toffanin et al., 2013). These studies formed the basis for higher biostratigraphic
resolution leading to definition of a new nannofossil biozonation (Agnini et al., 2014). In this study, we investigate
the middle Eocene-lower Oligocene sediments from ODP Hole 709C (ODP Leg 115) by means of calcareous
nannofossils and magnetostratigraphy.
Ocean Drilling Program (ODP) Site 709 was located in the equatorial Indian Ocean and biostratigraphy has been
investigated in the nineties (Okada, 1990; Fornaciari et al., 1990) while paleomagnetic data from the Initial Report
provided only a poorly constrained magnetostratigraphic interpretation, thus the cored succession was dated only
by means of biostratigraphy.
Our goal is to test the reliability in the Indian Ocean of the biohorizons recently identified at Site 711 (Fioroni et
al., in press), by means of high resolution sampling, new taxonomic updates, quantitative analyses on calcareous
nannofossils allowed to increase the number of useful bioevents and to compare their reliability and synchroneity.
The new magnetostratigraphic analyses and integrated stratigraphy allow also to achieve an accurate biochronology
of the time interval spanning Chrons C20 (middle Eocene) and C12 (early Oligocene).
In addition, this equatorial site represents an opportunity to study the carbonate accumulation history and the
large fluctuations of the carbonate compensation depth (CCD) during the Eocene (e.g. Pälike et al., 2012). The
investigated interval encompasses the Middle Eocene Climatic Optimum (MECO), and the long cooling trend
that leads to the Oligocene glacial state. By means of our new bio-magnetostratigraphic data and paleoecological
results we provide further insights on nannofossil assemblage response to the paleoclimatic changes that led to the
Oligocene glacial stat
Integrated magnetobiostratigraphy at the Oligocene/Miocene transition in the southwestern Atlantic Ocean (DSDP Leg 72, Hole 516F)
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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
Magnetobiostratigraphic chronology of the Eocene–Oligocene transition in the CIROS-1 core, Victoria Land margin, Antarctica: Implications for Antarctic glacial history
No full textIn 1986, cores were obtained to a depth of 702 m (with 98% recovery) from the CIROS-1 drill hole beneath the Ross Sea on the Victoria Land margin. Glaciogene sediments identified near the base of the hole mark the earliest known record of Antarctic glaciation. Initial biostratigraphic analysis indicated that the lower 336 m of the core is early Oligocene in age, and that the upper 366 m is of late Oligocene–early Miocene age. Recently, the chronology of the CIROS-1 core has been questioned. We developed a magnetostratigraphy for the lower 400 m of the CIROS-1 core to clarify the chronology. Our magnetobiostratigraphic results indicate that the base of the CIROS-1 core is early-late Eocene in age (corresponding to Chron C16r; ca. 36.5 Ma). We identify the Eocene-Oligocene boundary at about 410–420 m, within a 20-m-thick, poorly stratified, bioturbated sandy mudstone. This makes the CIROS-1 core the highest latitude site (77.1°S) from which this datum event has been recognized. At 366 m, a 4 m.y. hiatus, which lies immediately beneath fluvial sediments, accounts for most of Chrons C11 and C12. We recognize three major climatic episodes in the CIROS-1 core: (1) the late Eocene (34.5–36.5 Ma, 430–702 m), when relatively warm conditions dominated and there were high sedimentation rates and some glacial activity; (2) the late Eocene–early Oligocene boundary interval (28.5–34.5 Ma, 340–430 m), which was a transition from relatively warm to cooler conditions that coincided with glacial intensification, sea-level fall, and subaerial erosion of the shelf; and; (3) the late Oligocene – early Miocene (22–28.5 Ma, 50–340 m), when large-scale glaciation dominated the region and glaciers grounded across the continental shelf. From correlation with global oxygen isotope and sea-level records, we infer that the Antarctic climate and surrounding oceans cooled after separation of Australia and Antarctica and development of deep-water circulation between them. This marked the onset of the Eocene–Oligocene transition at ca. 34.5 Ma. A major East Antarctic ice sheet did not develop until the early-late Oligocene boundary, toward the end of the Eocene–Oligocene transition (ca. 28.5 Ma). Outlet glaciers did not breach the Transantarctic Mountains and ground across the Ross Sea Shelf until 0.5 m.y. later (ca. 28 Ma)
Environmental magnetic record of Antarctic palaeoclimate from Eocene/Oligocene glaciomarine sediments, Victoria Land Basin
No full textThe onset of continent-wide glaciation in Antarctica is still poorly understood, despite being one of the most important palaeoclimatic events in the Cenozoic. The Eocene/ Oligocene boundary interval has recently been recognized as a critical time for Antarctic climatic evolution, and it may mark the preglacial-glacial transition. Magnetic susceptibility, intensity of natural and artificial remanences, hysteresis parameters and magnetic anisotropy of the lower half ( late Eocene/early Oligocene) of the CIROS-1 core (from McMurdo Sound, Antarctica) reveal alternating intervals of high and low magnetic mineral concentrations that do not correspond to lithostratigraphic units in the core. Pseudo-single-domain magnetite is the main magnetic mineral throughout the sequence, and sharp changes in magnetite concentration match changes in clay mineralogy beneath and at the Eocene/Oligocene boundary. The detrital magnetite originated from weathering of the Ferrar Group (which comprises basic extrusive and intrusive igneous rocks). Weathering processes and input of magnetite to the Victoria Land Basin were intense during periods when the Antarctic climate was warmer than today, but during intervals when the climate was relatively cool, chemical weathering of the Ferrar Group was suppressed and input of detrital magnetite to the Victoria Land Basin decreased. Our results also indicate that a cold and dry climate was not established in Antarctica until the Eocene/Oligocene boundary, with major ice sheet growth occurring at the early/late Oligocene boundary. Some earlier cold intervals are identified, which indicate that climate had begun to deteriorate by the middle/late Eocene boundary
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
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