1,721,055 research outputs found
A 3D lithosphere-scale model of the Barents Sea and Kara Sea region
No full textThe Barents Sea and Kara Sea encompass one of the wide shelf margins of the Arctic Ocean. Since the 70-ies, scientific and economic studies contributed to a comparatively broad geological and geophysical database with regard to the remaining Arctic. A dense grid of seismic reflection profiles and few deep seismic refraction profiles clearly image that subregions experienced fundamentally different modes of basin formation. Extrapolation of structural geological information from onshore geology implies the presence of different tectonic provinces as a result from Precambrian to Paleozoic basement amalgamation. The deep crustal and lithospheric structure is only insufficiently imaged by seismic data across the Barents Sea and Kara Sea and the spatial extent of orogenic provinces and their potential influence on different stages of basin evolution from Paleozoic to early Cenozoic times remains only poorly understood. Therefore, the scope of this PhD thesis is to develop a 3D lithospheric model that captures first-order structural, compositional and thermal information on the sediments, the crystalline crust and the lithospheric mantle to understand the main factors controlling the evolution of these basins. Published datasets on the structural configuration, on physical properties and the temperature distribution are available but heterogeneously distributed across the study area. Therefore, a 3D modelling workflow is established. In a first step, all available geological and geophysical data, including interpreted seismic refraction and reflection data, seismological data, geological maps and previously published 3D models are integrated into one consistent model. This approach provides several advantages. The geological model can be constrained in more detail for regions where different types of observations exist such as for the top basement. In addition, the interpretation of coarsely scattered data can essentially be improved by applying physical principles in the frame of 3D gravity modelling in underexplored regions. In this context, 3D gravity modelling was used to constrain the configuration of the continental upper and lower crust. The final model resolves four major megasequence boundaries (earliest Eocene, mid-Cretaceous, mid-Jurassic and mid-Permian), the top crystalline crust, the top of the lower continental crust, the Moho and a newly calculated lithosphere–asthenosphere boundary. In addition, the 3D gravity modelling approach provides the base for a lithology-controlled parameterization of the crust (with mechanical and thermal properties) to allow for 3D calculations of the conductive thermal field and strength of the lithosphere. The structural and physical configuration of the lithosphere correlates with the orogenic and subsidence history of the Barents Sea and Kara Sea region. The southwestern Barents Sea is underlain by a thinned lithosphere (80 km) and high geothermal gradients as the result of multiple Phanerozoic rifting episodes. Thereby, rifting followed predominantly the Caledonian grain and culminated in the opening of the NE Atlantic from Paleocene/Eocene times on. Net horizontal forces exerted by the mid-oceanic ridge are high enough in Miocene times to overcome the lithospheric strength and could explain compressional deformation along the Vestbakken margin and at the Bjørnøyrenna Fault Complex in the western Barents Sea as observed in seismic lines. Thinnest continental lithosphere is present below northwestern Barents Sea including Svalbard (60 km), where late Cenozoic uplift was most pronounced. The East Barents Basin is assumed to encompass Timanian basement. The lithosphere thickens in two major steps to 150 km and follows the curvature of Novaya Zemlya. This correlation indicates that the lithosphere was possibly reworked during the Uralian collision. Elevated mantle densities as observed below the eastern Barents Sea seem to isostatically compensate thicknesses of the less dense sediments. This spatial relationship further exposes mantle density variations as a driving force for significant late Permian–earliest Triassic subsidence. Similar lithospheric thicknesses are found in the northern Kara Sea, which is also probably underlain by Timanian basement. Thickest lithosphere (200 km) and elevated upper mantle velocities distinguish the South Kara Basin from the surrounding regions. The positive mantle velocity anomaly may indicate a different upper mantle composition and support the affinity to the Siberian Craton. Beyond the discussion of the basin history, the shallow thermal and pressure configuration of the sediments was extracted to calculate the potential gas hydrate distribution at present-day and future alterations with regard to ocean warming. The modelling results show that thickest potential gas hydrates at present-day occur along the western Svalbard continental margin where their existence was revealed by numerous bottom-simulating reflectors in seismic profiles. Considering moderate ocean warming models, the gas hydrate stability zones along the continental margin will thin by several tens of meters within the next 100 years. In summary, this thesis demonstrates that the 3D lithospheric model is consistent with geological and geophysical data and reproduces independent observables including the gravity and thermal fields. The model is the first one to link the deep and shallow lithospheric structural and physical configuration with tectonic processes both onshore and offshore across the Barents Sea and Kara Sea region. The derived thermal field and rheological configuration could potentially serve as boundary condition for new projects covering different spatial scales including plate tectonic models as well as high-resolution basin models and geothermal projects
Replication Data for: Coupling crustal-scale rift architecture with passive margin salt tectonics: a geodynamic modelling approach
No full textGeodynamic Numerical model outputs (animations) of paper "Coupling crustal-scale rift architecture with passive margin salt tectonics: a geodynamic modelling approach". Submitted for Review.
These novel numerical models are generated by arbitrary Lagrangian‐Eulerian (ALE) thermo-mechanically coupled finite element method for the solution of plane strain, incompressible viscous‐plastic creeping flows. The method solves the force balance equations of equilibrium for quasi‐static incompressible flows (Stokes) in two dimensions coupled with time-dependent heat conservation equations. The mechanical and thermal evolution is coupled through nonlinear temperature- and pressure-dependent rheologies in addition to the temperature dependence of buoyancy.
The models are designed using a rheologically layered lithosphere comprising a 35 km‐thick crust and a 90 km mantle lithosphere above a sublithospheric mantle in a 600 km‐high and 1,200 km‐wide model domain. The Eulerian grid consists of 2,400 in horizontal and 290 elements in vertical directions. The distribution of the elements in the vertical direction is irregular, allowing for high resolution in the upper crust of Δz=200 m in the shallowest 20 km, Δz=625 m between 20 and 70 km, Δz=1,100 m between 70 and 120 km, and Δz=7,917 m between 120 and 600 km of depth. The resolution in the horizontal direction is 500 m for the entire model domain. Extensional horizontal velocity conditions (v = ±0.5 cm/year) are applied to the lithosphere, and the corresponding exit flux is balanced by a low-velocity inflow in the sublithospheric mantle. The top of the model is a free surface, and the sides and base are free slip boundaries.
The crust follows a wet quartz (WQ) rheology with different scaling factors (fc) as a way to test variable crustal strength. We use four contrasting crustal with variable fc from 30, 1, 0.1, and 0.02 for strong, intermediate, weak, and very weak crusts, respectively. These results in distinct thicknesses of the frictional‐plastic upper crust that range from 25 km, 15, 11, to 8 km. The densities of crust, mantle lithosphere, and sub-lithospheric mantle are calibrated so that the depth of the modelled mid-ocean ridge spreading system fits with global observations of average mid-ocean ridge depth. Salt is treated as a linear viscous material and all models have a constant salt viscosity (see ReadMe). Sedimentation occurs by filling all accommodation between the model surface and a defined base(sea)-level with sediments at each time step. We implement two different styles of sedimentation in our models, aggradation for syn-rift clastics and salt, and post-rift progradation using a dynamic depositional profile. We also apply a new novel tracking method based on Lagrangian surface descriptions that allow resolving the internal stratigraphic architecture of the salt and post-salt intervals with greater detail than in previous studies.
Models demonstrate the genesis and evolution of salt-bearing rifted margins and investigate the interplay between rifted margin architecture, late syn-rift salt deposition, and post-rift salt tectonics. We focus on four different types of continental margins: i) narrow, ii) intermediate, iii) wide, and iv) ultra-wide margins. We evaluate the: 1) interplay between laterally variable syn-rift extension, salt deposition and deformation, 2) influence of syn-rift basin architecture on post-rift salt flow, 3) spatial and temporal distribution of salt-related structural domains, and 4) contrasting styles of salt tectonics for different margin types. Narrow and intermediate margins form partially-isolated salt basins associated with prominent base-salt relief, limited translation but significant diapirism, and minibasin development. Wide and ultra-wide margins form wide salt basins with subtle base-salt relief that results in significant seaward salt expulsion and overburden translation. These wide margins demonstrate significant updip extension with the development of post-rift normal faults and rollovers, mid-margin translation associated with complex diapirism and downdip diapir shortening. All margins contain a distal salt nappe that varies in width and complexity. We also test the effect of different salt viscosities, relative post-salt progradation rates, and pre-salt sediment thicknesses. The results can be directly compared to several examples of salt-bearing rifted margins and provide an improved understanding of their dynamics and controls on the variability of salt tectonics
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
Background data for: "Geodynamic Models of Late-Syn- to Post-rift Salt Tectonics on Wide Rifted Margins - Insights from Geodynamic Modelling"
No full textGeodynamic Numerical model outputs (animations) of "Late-Syn- to Post-rift Salt Tectonics on Wide Rifted Margins - Insights from Geodynamic Modelling" (Tectonics, 2022)
The geodynamic models of lithosphere extension and post-rift salt tectonics quantify different types of salt flow on rifted margins and test the effects of different salt viscosities (low, intermediate and high) on salt tectonics and margin evolution.
The models show that updip extension balances largely with downdip diapir shortening, but that the distal salt nappe advance is largely unrelated to these processes. The salt nappes form by a combination of late syn-rift salt stretching and post-rift pressure-driven salt flow. This implies that the present-day width of salt nappes cannot be used as a constraint to balance updip extension on salt-bearing rifted margins. These observations have important implications for kinematic reconstructions of salt tectonics along rifted margins based on the common assumption of balanced salt deformation and for understanding the relationship between the distal edge of the salt basin and continent-ocean boundaries, important for plate-kinematic reconstructions.
Salt tectonics in all models exhibits three characteristic phases. 1) Syn-depositional salt flow and development of syn-salt-deposition minibasins resulting from stretching in the distal margin as salt is deposited during the last phase of rifting. 2) Emplacement of distal salt nappes on the early oceanic crust by stretching above the rift axis. 3) Post-rift sediment progradation and significant salt tectonics in the form of updip extension, translation, downdip diapir shortening, and pressure-driven salt flow and nappe advance. The occurrence of these distinct deformation processes (e.g., updip extension, translation, downdip shortening, syn-rift nappe stretching and post-rift nappe advance) is independent of salt viscosity, however, their magnitude, timing, as well as the style of salt deformation, vary.
Our models improve the current understanding of the dynamics of salt tectonics along rifted margins and the interplay between rifting and syn- to post-rift salt deformation associated with late syn-rift salt basins. The models are comparable to various examples of wide salt-bearing rifted margins such as the Brazilian, parts of West Africa, and Gulf of Mexico salt basins. They reproduce their observed crustal-scale architecture, regional salt tectonics styles, distribution of structural domains, and magnitudes of deformation
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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