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Diffuse Cretaceous-Cenozoic rifting in the Southern Ross Sea: the influence of inheritance and kinematics
No full textContinental Rift systems often involve narrow regions, which accommodate all the stretching. In some cases, the initial extension occurs with a diffuse style and may successively produce a narrow rift. An example is the West Antarctica Rift System, bearing evidence of the concurrent formation of multiple basins normal to the rift axis. This rift system has undergone extension between the Cretaceous and the middle Neogene age (105 to 11 Ma [1, 2]), due to the sea floor spreading in the northwestern Ross Sea. It is composed of three main basins (Victoria Land Basin, Central Trough, and Eastern Basin), which cover a present-day length of 900-1000 km, encompassing the lateral contact between the cratonic domains of East Antarctica and West Antarctica Phanerozoic lithosphere. The different basins, bounded by structural highs, exhibit significant variations in the thickness and thinning of the underlying crust and lithosphere. This multiple-basin pattern suggests that, at least for some part of the rifting, the deformation occurred in a diffuse way, instead of being localized in a small portion of the rift system [3].
The factors controlling these deformation styles have been identified in the inheritance of structures and thermal/rheological heterogeneities [4], which acted concurrently with the extensional kinematics in shaping the present-day rift architectures. Therefore, an improved knowledge on how different thermo-structural initial conditions (e.g. lateral contacts, thermal transients, accumulated strain softening) influence the outcome of rifting may help identify the most likely state at the onset of rifting. To this purpose, we implement a series of numerical models, testing several starting structural conditions (rheology, temperature, prior damage) and distribution of extensional velocity (a single phase or multiple pulses, for the same total extension) that could trigger this peculiar diffuse deformation pattern.
To build a 2-D simplified geometry of the structures of the rift system, we took as a reference the seismic profiles BGR-02 and ACRUP2, normal to the rift axis, along the 77° S parallel [5]. We assumed an initial crustal thickness of about 50 km and a kinematic pattern consisting of two main distinct extension phases, covering the Cretaceous-Cenozoic interval [1, 6].
Modelling was carried out using the open source Underworld2 code [7], which relies on Lagrangian integration point finite element approach and provides a Python API to construct, run, and visualize the output of geodynamic models. The results show that the models that are more consistent with the observations require the existence of peculiar a-priori inherited features. In addition to the role of inheritance, diffuse patterns are favoured, for the same extension amount, by slow and long-lasting rifting phases, with respect to fast and short time pulses.
This work was carried out in the context of PNRA project "Onset of Antarctic Ice Sheet Vulnerability to Oceanic conditions (ANTIPODE)".
[1] Behrendt et al. (1991) https://doi.org/10.1029/91TC00868
[2] Granot & Dyment (2018) https://doi.org/10.1038/s41467-018-05270-w
[3] Huerta & Harry (2007) https://doi.org/10.1016/j.epsl.2006.12.011
[4] Perron et al. (2021) https://doi.org/10.1051/bsgf/2020038
[5] Trey et al. (1999) https://doi.org/10.1016/S0040-1951(98)00155-3
[6] Davey & De Santis (2006) https://doi.org/10.1007/3-540-32934-X_38
[7] Mansour et al. (2020) https://doi.org/10.21105/joss.0179
The Ross Sea formation: enquiring the sensitivity of basin architecture to prior conditions, with numerical models and a parameter search
No full textThe basins composing the 1000-km wide West Antarctica Rift System (WARS), derived from extensional dynamics lasting from the Cretaceous to the Middle Neogene, bear evidence of a peculiar evolution through time: a transition from a diffuse to a localized thinning style and a migration of the focus of deformation, which likely progressed towards the cratonic domains of West Antarctica. Using the current observations, we aim at identifying which inherited starting conditions [1] result in outcomes compatible with the present-time structures and which do not allow so, unless other factors are accounted for.
To this aim, we turn to an extensive grid search in the parameter space, running a large number of forward numerical models to cover the possible permutations of parameters under test. We use the open source Underworld2 code [2] with a simplified scheme of starting conditions and kinematics boundaries, for lithospheric-scale 2-D thermomechanical models. We analyse the results obtained by changing a great number of parameters, including initial geometries of the crust and lithosphere, different rheologies, inherited structures, such as strain-weakening scars and thermal remnants of slabs.
We identify that a high crustal thickness (more than 45 km) is required to accommodate the first rifting phase (170 km ca. of cumulated extension, [3]) without producing crustal necking and eventual ocean formation. Parameters that favour a weaker strength profile, chiefly temperature (due to a thicker crust and/or a shallow lithosphere-asthenosphere boundary), are also required to avoid an early transition to localized deformation, in agreement with previous studies [4]. Smaller scale features, such as partition in multiple sub-basins, require additional factors, such as inherited weak-zone seeds (“scars”) in the crust and mantle, which are likely remnants of previous compressive phases [5].
[1] Perron, P., Le Pourhiet, L., Guiraud, M., Vennin, E., Moretti, I., Portier, É., & Konaté, M. (2021). Control of inherited accreted lithospheric heterogeneity on the architecture and the low, long-term subsidence rate of intracratonic basins. BSGF - Earth Sciences Bulletin, 192. https://doi.org/10.1051/bsgf/2020038
[2] Mansour, J., Giordani, J., Moresi, L., Beucher, R., Kaluza, O., Velic, M., Farrington, R., Quenette, S., & Beall, A. (2020). Underworld2: Python Geodynamics Modelling for Desktop, HPC and Cloud. Journal of Open Source Software, 5(47), 1797. https://doi.org/10.21105/joss.01797
[3] Brancolini, G., Busetti, M., Coren, F., De Cillia, C., Marchetti, M., De Santis, L., Zanolla, C., Cooper, A.K., Cochrane, G.R., Zayatz, I., Belyaev, V., Knyazev, M., Vinnikovskaya, O., Davey, F.J., Hinz, K., 1995. ANTOSTRAT Project, seismic stratigraphic atlas of the Ross Sea, Antarctica. In: Cooper, A.K., Barker, P.F., Brancolini, G., (Eds.), Geology and Seismic Stratigraphy of the Antarctic Margin. Antarctic Research Series, vol. 68, https://doi.org/10.1029/AR068
[4] Huerta, A. D., & Harry, D. L. (2007). The transition from diffuse to focused extension: Modeled evolution of the West Antarctic Rift system. Earth and Planetary Science Letters, 255(1–2), 133–147. https://doi.org/10.1016/j.epsl.2006.12.011
[5] Talarico, F., Ghezzo, C., & Kleinschmidt, G. (2022). The Antarctic Continent in Gondwana: a perspective from the Ross Embayment and Potential Research Targets for Future Investigations. In Antarctic Climate Evolution (pp. 219–296). Elsevier. https://doi.org/10.1016/B978-0-12-819109-5.00004-
Studio multidisciplinare per ricostruire l’evoluzione del Glomar Challenger Trough e dell’area di scarpata (Mare di Ross Orientale, Antartide) durante il tardo Quaternario
No full textLa calotta glaciale antartica occidentale (West Antarctic Ice Sheet, WAIS) è avanzata e si è ritirata numerose volte durante i diversi periodi glaciali ed interglaciali. La presenza di morfologie glaciali e subglaciali sulla piattaforma continentale indica che la calotta è avanzata fino al margine della piattaforma continentale in diversi settori del Mare di Ross orientale (Eastern Ross Sea, ERS) durante l’Ultimo massimo glaciale (Last Glacial Maximum, LGM). La storia del Mare di Ross è ancora incerta, in particolare le tempistiche del ritiro della calotta alla fine dell’LGM. I sedimenti depositati sulla piattaforma e sulla scarpata continentale durante il tardo Quaternario possono aiutare a ricostruire l’evoluzione della calotta durante questo periodo fondamentale. Lo scopo di questo lavoro è di ricostruire l’evoluzione della WAIS nel Glomar Challenger durante il tardo Quaternario. Questa è un’area fondamentale perché l’ERS è stato meno studiato rispetto al Mare di Ross occidentale, ma anche perché il Glomar Challenger è una delle vie attraverso cui l’acqua profonda circumpolare (Circumpolar Deep Water, CDW) raggiunge la parte interna della piattaforma continentale.
Le cinque carote e i tre box core scelti per questo lavoro sono stati ottenuti nel corso di diverse campagne PNRA (1995-1996, 1998-1999 e 2013-2014). Per studiarle è stato adottato un approccio multidisciplinare usando una combinazione di analisi sedimentologiche, micropaleontologiche (foraminiferi), chimiche e geochimiche (XRF core scanner, biomarkers) e datazioni al radiocarbonio fatte sulla sostanza organica. Queste carote e box core sono già stati in parte studiati, ma l’aggiunta di altre analisi, l’applicazione di nuove metodologie e l’incremento della risoluzione stratigrafica sono utili per ricostruire le dinamiche della calotta durante il tardo Quaternario.
Questo lavoro è supportato da due progetti:
-STREAM (Evoluzione tardo quaternaria dell’interazione oceano – calotta glaciale: la registrazione nel margine continentale del Mare di Ross, Antartide. Periodo 2019 – 2021. Finanziato dal Ministero degli Affari Esteri e della Cooperazione Internazionale (MAECI) e dalla Fondazione Nazionale della Ricerca (NRF) della Corea del Sud).
-ANTIPODE (Esordio della vulnerabilità della calotta glaciale antartica alle condizioni oceaniche. Periodo 2020 – 2022. Finanziato dal PNRA
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
Polar region on a changing planet: learning from the past, exploring the future
No full textSessione S 15. Polar region on a changing planet: learning from the past, exploring the future
The polar areas are complex, interlinked systems whose environmental changes driven by climate variations have a fundamental impact on the rest of the planet. Ice melting associated to increasing atmospheric and ocean surface temperatures, is responsible for progressive sea level rise threatening coastal urbanization and infrastructures, and alteration of the atmosphere-ocean coupling system responsible for precipitation patterns around the world.
The information about past climate changes are especially guarded in the glacial and geological records of the polar areas, very sensitive also to small temperature changes which can lead to large environmental feedback.
This session welcomes contributions reporting the state-of-the-art in polar sciences, including geology, oceanography, glacial geology and geomorphology, glaciology and related modelling exploring the future climatic trend of polar region
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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