1,721,025 research outputs found
Sill emplacement and contact metamorphism in a siliciclastic reservoir on Svalbard, Arctic Norway
No full textSill emplacement and contact metamorphism in a siliciclastic reservoir on Svalbard, Arctic Norway
No full textIgneous intrusions in sedimentary basins are associated with contact aureoles that influence rock properties such as maturation, porosity and permeability. On Svalbard, an extensive dolerite complex (i.e., the Diabasodden Suite) was emplaced in a heterolithologic sandstone, siltstone, shale and carbonate succession during the Early Cretaceous (c. 124.5 Ma). The sedimentary host rocks include the predominantly siliciclastic, Upper TriassicMiddle Jurassic Kapp Toscana Group, which is currently being investigated as a storage unit for potential CO2 sequestration in the vicinity of Long yearbyen. As part of the baseline reservoir characterisation, a 2.28 metre-thick dolerite sill and its associated contact aureole was drilled and fully cored in the lower part of the target aquifer. Geochemical data indicate that the intrusion belongs to the Diabasodden Suite, which also crops out 18 km from the planned injection site. Samples spanning the contact aureole show significant thermal effects around the thin sill. The total organic carbon content is lowered towards the contact (from 1-2 wt.% to zero) accompanied by a reduction of the pyrolysis output and higher Tmax values (500°C vs. 320°C). A count of the visual fractures along the Dh4 borehole shows that the sill itself is characterised by a fracture frequency of 8-10 fractures per metre, well above the background fracturing in the host rock above the sill (0-1 fractures per metre). Increased background fracturing (4-10 fractures per metre) is, however, evident in the host rock below the sill. Our results show that the total aureole thickness is 160-195% of the sill thickness and that the sill and aureole together represent a six metre-thick geochemical and mechanical perturbation in the sedimentary succession. We conclude that even very thin sills and related aureoles may affect the CO2 storage aquifer by locally reducing porosity in the host rock, but also by enhancing permeability along the fractured intrusion-host rock interfaces
Late Mesozoic magmatism in Svalbard: A review
No full textLate Mesozoic mafic igneous rocks are widespread across the Arctic region, and are collectively referred to as the High Arctic Large Igneous Province (HALIP). In Svalbard the HALIP is represented by the Diabasodden Suite, an extensive system of predominantly basic intrusive doleritic rocks. Associated lava flows are exposed on the far east of the archipelago. Two main igneous centres have been proposed: (1) Central Spitsbergen and (2) the eastern Svalbard dolerite belt, spanning Hinlopenstretet and the islands of Edgeøya and Barentsøya. Offshore seismic and magnetic data suggest a link between the Svalbard and Franz Joseph Land igneous exposures. Intrusions occur predominantly as sills, up to 100. m thick and laterally continuous for up to 30 km. Dykes are present locally, and range in thickness from < 10 m up to 100 m. A compilation of published geochemical data reveals that the vast majority of samples have a basaltic geochemical signature. Comparison to HALIP rocks elsewhere in the Arctic, including paleotectonic reconstructions, suggests that the Diabasodden Suite formed as part of an intra-plate basaltic complex originating from a source near the Alpha Ridge. Apart from Late Mesozoic magmatism, Svalbard has also experienced magmatic activity both before and after the intrusion of the Diabasodden Suite dolerites. These are distinguished on the basis of their geochemical signature and timing. Timing of the Diabasodden Suite magmatism is currently poorly constrained. More than 130 radiometric (Ar-Ar and K-Ar) ages have been published, with a wide range of ages (ca. 75-145 Ma). Modern radiometric dating (U-Pb) on three samples suggests a shorter-lived intrusion pulse at ca. 124.5 Ma (i.e. early Aptian). While much work has been conducted on the Diabasodden Suite in the past, a detailed synthesis of this widespread unit is presently missing. In this contribution we discuss the current knowledge on the Diabasodden Suite, synthesizing and reviewing the past studies as well as pointing out possible future research directions
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
Seismic volcanostratigraphy of the Norwegian Margin: constraints on tectono-magmatic break-up processes
No full textVoluminous volcanism characterized Early Tertiary continental break-up on the mid-Norwegian continental margin. The distribution of the associated extrusive rocks derived from seismic volcanostratigraphy and potential field data interpretation allows us to divide the Møre, Vøring and Lofoten–Vesterålen margins into five segments. The central Møre Margin and the northern Vøring Margin show combinations of volcanic seismic facies units that are characteristic for typical rifted volcanic margins. The Lofoten–Vesterålen Margin, the southern Vøring Margin and the area near the Jan Mayen Fracture Zone show volcanic seismic facies units that are related to small-volume, submarine volcanism. The distribution of subaerial and submarine deposits indicates variations of subsidence along the margin. Vertical movements on the mid-Norwegian margin were primarily controlled by the amount of magmatic crustal thickening, because both the amount of dynamic uplift by the Icelandic mantle plume and the amount of subsidence due to crustal stretching were fairly constant along the margin. Thus, subaerial deposits indicate a large amount of magmatic crustal thickening and an associated reduction in isostatic subsidence, whereas submarine deposits indicate little magmatic thickening and earlier subsidence. From the distribution of volcanic seismic facies units we infer two main reasons for the different amounts of crustal thickening: (1) a general northward decrease of magmatism due to increasing distance from the hot spot and (2) subdued volcanism near the Jan Mayen Fracture Zone as a result of lateral lithospheric heat transport and cooling of the magmatic source region. Furthermore, we interpret small lateral variations in the distribution of volcanic seismic facies units, such as two sets of Inner Seaward Dipping Reflectors on the central Vøring Margin, as indications of crustal fragmentation
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
High-velocity breakup-related sills in the Vøring Basin, off Norway
No full textMultichannel seismic reflection profiles in the Hel Graben, V0ring Basin, reveal a sill complex at approximately 5 km depth. It is associated with exceptionally high, 7.4 km s−1, seismic wide-angle velocities. The existence of observable wide- angle arrivals shows that the sills act as efficient waveguides. Seismic reflection data and amplitude modeling constrain the thickness of individual sills to approximately 100 m. Sonic logs from sills of similar thickness on the nearby Utgard High show an average velocity of 7.0 km s−1. Such high velocities require an olivine-gabbroic sill composition and emplacement under conditions which allowed growth of relatively large crystal sizes. A possible reason for such an emplacement environment is the HeI Graben's role as an intrusion center during breakup volcanism. This would provide the necessary duration of the magmatic activity as well as locally increased melt volumes and cooling times. Sill complexes of this kind decrease the accuracy of determined velocity fields and crustal geometries below the top of the sill complex, affecting depth conversion and gravity modeling. Furthermore, the results question the concept of lower crustal bodies as large-scale, homogeneous accumulations of mafic melt
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