1,720,984 research outputs found
Overview on the stratigraphic and sedimentological features of the Permian-Mesozoic continental successions in Northern Victoria Land (Transantarctic Mountains, Antarctica)
No full textThe Gondwana successions in Antarctica unconformably overlain the Ross Orogen terranes and are widespread throughout the whole Transantarctic Mountains. They are mainly represented by the siliciclastic Devonian-Jurassic Beacon Supergroup and the Jurassic Ferrar Dolerite-Kirkpatrick Basalt. In Northern Victoria Land (NVL), they occur with variable age and thickness, ranging from few tens of meters to 300 m. The outcrops are scattered in two wide regions including the lowerRennick Glacier (studied in the 80s by USA-NZ-AUS and german teams) and the lower Priestley and Campbell glaciers studied in the 90s by italian teams. According to many authors, the clastic successions of the NVL, called Takrouna Fm. (Permian) in the northernmostoutcrops and Section Peak Fm. (Triassic-?Jurassic) inthe southernmostones, represent the siliciclastic, mainly cross-bedded sandstone infilling of alluvial Permo-Triassic basin systems, and corresponding to the prolongation to the north of the wider basin system, located in Southern Victoria Land, of the Beacon Supergroup. It is worth to note that the age of the latter formation is not well constrained, because, despite the presence of Triassic paleoflora and trace fossils, the relationships with the overlying middle Jurassic lava beds, dykes and sills are not well defined.
These formations show a general flat-bedding attitude, and they unconformably overlain the basement formed of metamorphic and intrusive rocks of the Wilson Terrane, through a regional erosional surface called “sub-Beacon Peneplain”.
For this overview, based on available previous geological maps and on a new survey performed during the 2012/13 Italian Antarcticexpedition, we have investigated many of the NVL Beacon-like outcrops, which are greatly scattered, due to their low-thickness and ice cover. These factors make difficulties for a high-resolution bed-correlation, but a stratigraphic-sedimentological architecture frame can be tentatively defined. To this aim, sedimentological facies and petrographical analyses have been preliminary performed and will be developed in the next steps of the research. In the Rennick Glacier area, the base of the siliciclastic succession may consist ofa 20-50 m thick diamictite-fluvioglacial horizon. The clastic successions comprise a wide spectrum of coarse sedimentary facies, with dominant pebbly to coarse sandstones with trough or planar cross-bedding, and subordinate massive microconglomerates, massive and normal graded sandstones, carbonaceous mudstones with fossil leave impressions and trunk remains, coal deposits. The sandstone composition, reveals high maturity, containing mainly quartz and feldspar clasts, with minor lithic fragments, ranging from quartzarenite to subarkose to arkose, whereas the upper portion of the westernmore successions show significant volcanic clastic content, so to define volcanic-bearing lithic arkoses. Palaeocurrent data show a north to northwest wide dispersion.
The depositional system agrees with a wide alluvial plain characterized by large and deep rivers with braided to meander style, compatible with the sandy-braided model (similar to the deep perennial braided “S. Saskatchewan type” of Miall), forming compound bars with sandy bedforms and downstream accretion macroforms, infilling a plain close to a high to moderate morphological gradient area. The thickness differences between southern and northern sectors of the NVL, allow to define a basin variability and splitting, due to the tectonic rifting processes, starting during Triassic with the formation of the Rennick Glacier “graben” and developing in the Jurassic with the volcanic activity
Cenozoic rejuvenation events of Massif Central topography (France): Insights from cosmogenic denudation rates and river profiles
No full textThe French Massif Central is a part of the Hercynian orogenic belt that currently exhibits anomalously high topography. The Alpine orogenesis, which deeply marked Western European topography, involved only marginally the Massif Central, where Cenozoic faulting and short-wavelength crustal deformation is limited to the Oligocene rifting. For this reason the French Massif Central is a key site to study short- and long-term topographic response in a framework of slow tectonic activity. In particular the origin of the Massif Central topography is a topical issue still debated, where the role of mantle upwelling is invoked by different authors. Here we present a landscape analysis using denudation rates derived from basin-averaged cosmogenic nuclide concentrations coupled with longitudinal river profile analysis. This analysis allows us to recognize that the topography of the French Massif Central is not fully equilibrated with the present base level and in transient state.Our data highlight the coexistence of out-of-equilibrium river profiles, incised valleys, and low cosmogenically derived denudation rates ranging between 40 mm/kyr and 80 mm/kyr. Addressing this apparent inconsistency requires investigating the parameters that may govern erosion processes under conditions of reduced active tectonics. The spatial distribution of denudation rates coupled with topography analysis enabled us to trace the signal of the long-term uplift history and to propose a chronology for the uplift evolution of the French Massif Central
Apatite Fission Track Signatures of the Ross Sea Ice Flows During the Last Glacial Maximum
No full textThe catchment for the Ross Sea ice includes both the East and the West Antarctic ice sheets, but the mass balance is a direct response to climate change. Our work is aimed to reconstruct the ice flows after the Last Glacial Maximum and is based on apatite fission track data from samples collected from 18 piston cores across the Ross Sea embayment. Fission track ages have been divided into meaningful populations and then compared with bedrock ages from West and East Antarctica. Furthermore, fission track lengths have been measured on each population and then compared through forward modeling with thermal histories derived from literature. The widespread presence of apatites with cooling ages of about 30–40 Ma reveals a main exhumation phase of the Transantarctic Mountains during the Oligocene associated to the last phases of the West Antarctic Rift System. Furthermore, the presence of key marker apatites (e.g., younger than 21 Ma or older than 230 Ma) allows to identify the Central High as a major ice flow divide
The topography of mountain front as expression of deep and surface earth processes: comparison between the central and southern Apennines (Italy)
No full textTectonic and climatic signals from apatite detrital fission track analysis of the Cape Roberts Project core records, South Victoria Land, Antarctica
No full textThe Cenozoic tectonic reorganization of the West Antarctic Rift System in the Ross Sea region occurred concurrently with a major change in the global climate system and a global reorganization of plate motions. This region thus provides the opportunity to study in detail a range of geological issues dealing with tectonic and climate feedbacks during the late Eocene/early Oligocene greenhouse/icehouse transition at high latitudes. With the aim to decipher tectonic vs. climatic forcing in the ice sheet drainage evolution, a detrital apatite fission track study was carried out throughout the Cenozoic drill-cored stratigraphic succession of the Cape Roberts Project (McMurdo Sound, Victoria Land Basin). Apatite fission-track ages of detrital samples, with de-positional ages between 34 Ma and 17 Ma, were decomposed into statistically significant age populations. Three age peaks were detected, reflecting different bedrock provenance areas: (i) a young peak (P1 between 34 Ma and 26 Ma) recording the signal of a source area exhumed with a constant denudation rate, but absent in the proximal continental area; and (ii) two peaks, older than 40 Ma, that are instead compatible with thermochronological data available from the onshore bedrock. P1 peak testifies a late Oligocene-early Miocene denudation event and traces a southern provenance of a fraction of the sediments filling the Cape Roberts Basin. We propose that this denudation event might have been triggered by renewed N-S transtensional shearing along the western shoulder of Victoria Land Basin, controlling glacial flow pattern and the associated sediment transport. (C) 2013 Elsevier B.V. All rights reserved
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
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