排序方式： 共有28条查询结果，搜索用时 31 毫秒
1.
Christoffer Oftedahl 《International Journal of Earth Sciences》1959,48(1):18-26
The Permian activity in the Oslo region started with lava effusions. Monzonitic rhomb porphyry flows predominate, with basaltic flows inbetween. Then a number of basalt volcanoes formed. This phase ended in explosive volcanism, producing ignimbrites, and the explosive activity is considered the primary cause for formation of at least four large and a few smaller cauldrons (or calderas). Below the lava surface monzonitic magma and associated syenitic and granitic magmas crystallized to larvikite, nordmarkitic and granitic rocks. These magmas are assumed to be formed by local melting of portions of the lower crust. The mode of emplacement is stoping. 相似文献
2.
Provenance and accumulation rates of opaline silica,Al, Ti,Fe, Mn,Cu, Ni and Co in Pacific pelagic sediments 总被引：2，自引：0，他引：2
Accumulation rates and chemical compositions have been obtained for pelagic sediments for 73 locations in the Pacific and for 11 in the Indian Ocean. The data for the Pacific show that many elements accumulate rapidly close to the continents and slowly in the central part of the ocean. This pattern is interrupted by two major zones of relatively high accumulation rates, one along the Equator and one along the East Pacific Rise. Deposition of opaline silica is almost completely restricted to areas of known high biological productivities at the Equator and at very high latitudes. Cu and Ni show stronger tendencies than Fe and Mn to precipitate with opaline silica. The highest accumulation rates of Fe and Mn in the open Pacific occur along the East Pacific Rise, to some extent also Cu and Ni are enriched there due to volcanic processes. Al and Ti show high accumulation rates only close to the continents; these elements appear to be almost completely terrigenous.Provenance studies of minerogen fractions, using the relations between Fe, Ti, Al and Mn, show that significant quantities of basaltic matter (oceanic crust) are incorporated into the sediments only in areas of very low total sedimentation rates in the vicinity of oceanic island groups such as Polynesia and Hawaii, whereas hydrothermal processes act as a major sediment source only on the East Pacific Rise. Sediments in the north as well as in the southernmost part of the Pacific are nearly entirely terrigenous. A balance estimate of the minerogen fraction of the deep-sea sediments from the open Pacific suggests that between 75 and 95% of all sediments in the Pacific are terrigenous and that submarine weathering (and release of basaltic debris in general) and submarine exhalations each account for only a small fraction of the sediments. 相似文献
3.
Christoffer Bostrm Emma L. Jackson Charles A. Simenstad 《Estuarine, Coastal and Shelf Science》2006,68(3-4):383
Seagrasses comprise some of the most heterogeneous landscape structures of shallow-water estuarine/marine ecosystems in the world. However, while knowledge at the molecular, organism, patch and community scale is pervasive, understanding of seagrass landscape ecology is more fragmentary and has not been synthesized. The growth and recruitment dynamics of seagrasses as well as man-made and/or natural disturbances create complex spatial configurations of seagrass over broad (metres to kilometres) spatial scales. Hence, it is important to identify mechanisms maintaining and/or threatening the diversity-promoting function of seagrass meadows and to understand their effects on benthic populations and communities. Although landscape ecology has recently become more integrated into seagrass research, our understanding of animal responses to variability in seagrass landscape structure is still fragmentary. By reviewing the literature to date, this paper evaluates studies on seagrass landscape ecology, testing the general null hypothesis that concepts developed in terrestrial settings can be generalized across landscapes, and (a) presenting definitions and terms used in seagrass landscape ecology, (b) reviewing geographical patterns of seagrass landscape studies to identify possible key regions and target species, (c) evaluating different methodological approaches, (d) describing the spatial and temporal scales used to describe organism responses to seagrass landscape structure, and (e) placing seagrass landscapes into an applied context. 相似文献
4.
5.
Prof. Dr. Christoffer Oftedahl 《International Journal of Earth Sciences》1967,57(1):203-218
Zusammenfassung Kartierung seit 1960 hat gezeigt, daß das Vestfold Lava-Gebiet im südlichen Teil des Oslo-Grabens stratigraphisch viel umfassender ist als früher gefunden. Zwar findet man hier 26 Lava-Ströme von Rhombenporphyr, 5 Basaltströme und 3 Trachytlaven. Jünger sind ungefähr 1000 m von Rhyolitströmen in der im Süden gelegenen Ramnes-Caldera. Noch jünger ist das große Larvikitfeld im südlichen Oslo-Gebiet. Ganz wie die Plutonite sich von intermediärer Zusammensetzung bis saurer bewegen, verändern sich auch gradweise die Vulkanite in ihrer Zusammensetzung von intermediärer bis saurer während des Larvikit-Magmatismus.Für die totale Magmenbildung des Oslo-Grabens gibt es im Lichte der letzten Ergebnisse aus dem Graben sowie aus der Literatur die folgenden Möglichkeiten: 1. Tiefkrustale anatektische Magmenbildung, die sich oben bewegt, mit gradweise saureren Produkten. 2. Tiefkrustale anatektische Magmenbildung begleitet von tiefkrustaler gravitativer Differentiation. 3. Tiefkrustale Magmenbildung mit weitgehender oberflächennaher Differentiation. 4. Basaltische Magmen aus dem oberen Mantel, die einer weitgehenden krustalen Differentiation unterliegen. 5. Mögliche Differentiation im oberen Mantel von Mantel-Magmen.
Mapping in the Vestfold lava area in the southern part of the Oslo Graben has revealed a lava stratigraphy consisting of 26 rhomb porphyry flows, 5 basalt lavas and 3 trachyte lavas. A thickness of about 1000 m of rhyolite flows within the Ramnes caldera is younger than the rhomb porphyries. Still younger is the large area of larvikite in the southernmost part of the Oslo Region. Thus the volcanics show a continuous series from intermediate to acidic composition just as the plutonic rocks, although all volcanic eruptions happened within the larvikite phase of the plutons.The magma formation within the Oslo Graben may be explained within the following possibilities: 1. Anatectic magma formation in the deeper crust, moving upwards and changing gradually to more acidic products. 2. Anatectic magma formation in the deeper crust, accompanied by gravitative differentiationin situ. 3. Magma formation in the deeper crust, with comprehensive differentiation near the surface. 4. Basaltic magmas from the upper mantle, undergoing a comprehensive crustal differentiation. 5. Possible differentiation in the upper mantle.
Résumé La documentation cartographique a montré que l'étendue de la lave de Vestfold au sud du fossé d'Oslo est beaucoup plus grande qu'où avait supposé jusqu'ici. On y trouve 26 courants de lave à rhombes porphyriques, 5 courants de basalte et 3 laves trachytiques. Les 1000 m de lave rhyolitique de la Ramnes-Caldera au sud sont plus récents. Encore plus récent est le vaste champ de larvikite au sud d'Oslo. Les plutonites changeaient d'une composition intermédiaire à une composition acide de même que les volcanites, mais celles-ci pendant le magmatisme du larvikite.La formation du magma dans le fossé d'Oslo pent être expliquée par les plus récents résultats du fossé ainsi que par la littérature. Les possibilités sont: 1. Formation anatectique de magma dans une croûte profonde qui monte et devient de plus en plus acide. 2. Formation anatectique de magma dans une croûte profonde accompagnée d'une différentiation gravitative in situ. 3. Formation de magma dans une croûte profonde à différentiation près de la surface. 4. Des magmas basaltiques du manteau supérieur sujets à une différentiation largement crustale. 5. Différentiation possible au manteau supérieur.
. 26 . 5 3 . . , , . .相似文献
6.
Suspended matter was collected at 30 stations in the Baltic and Kattegatt, at the thermocline and at the bottom, and analysed for Na, Ca, Mg, Si, Ti, Al, Fe, Mn, Ba, Sr, Ni and V. The composition of the suspended matter varies considerably, but can be described as a mixture of: (1) 12–25% terrigenous detritus with much Si, Al, Ti and Fe; (2) 75–88% biological matter with much Ni, V and Ba; and (3) some Mn-oxyhydroxide.The annual efflux of water from the Baltic is about 460 km3, with a suspended load in the Baltic straits of ～1.2–3.6 mg ash material l?1 These values imply that much Si, Ti, Al, Fe, Sr, Ni and V and particularly much Ba and Mn are lost from the Baltic in the suspended load.The average suspended matter is richer in Mn(5×), Ba(2.5×), Sr(4×) and V(1.8×) than permanently depositing Baltic sediments. These constituents are relatively enriched in pelagic deposits, i.e. it is likely that much Mn, Ba and V in deep-sea sediments derive from the continents via suspended transport. This conclusion is supported by the similarity between suspended matter and average Atlantic pelagic sediment. 相似文献
7.
8.
In the 200 km by 45 km area of exposed Permian rocks of the Oslo rift of southern Norway, 15 and possibly 18, cauldrons occur within a rift length of 180 km. These cauldrons range in size from 5 to 16 km in diameter and average around 10–12 km. They exhibit ring dikes, central intrusions, caldera depression deposits (ignimbrites, breccias, lake sediments), and cannibalism of the subsided block by younger, stoping plutons. Only six cauldrons retain most of their periphery, three have lost half their original area to younger plutons, and nine show up as segments or crescents.Ring dikes are mostly syenitic, and central intrusions range from monzonitic to syenitic, with some granitic plugs. The caldera blocks seem to have subsided into monzonitic magma chambers with a differentiated top layer of syenitic magma. Subsidence is assumed to have been started by large-scale crustal movements with a slight tensional component that produced subsidence in the uppermost parts of the magmatic plumbing system. Blocks having thicknesses of 2–5 km above these uppermost magma chambers dropped along sharp ring faults. Absence of resurgent domes is due to composition (and viscosity) of the underlying magmas: these intermediate magmas stoped their way up, without doming. Cauldrons with magmas of intermediate composition make up a major group, between the basaltic shield cauldrons and the resurgent type that produced ignimbrites. 相似文献
9.
Seasonal dynamics of a cyanobacteria-dominated microbial community in surface sediments of a shallow,eutrophic lake 总被引：16，自引：0，他引：16
Bengt Boström Anna-Kristina Pettersson Ingemar Ahlgren 《Aquatic Sciences - Research Across Boundaries》1989,51(2):153-178
The seasonal variation of microbial biomass and activity in the surface sediments (0–10 cm) of the shallow, eutrophic Lake Vallentunasjön was followed during one year. OverwinteringMicrocystis colonies dominated the microbial community during all seasons, constituting 60–90% of the total microbial biomass. Expressed on an areal basis, the benthic biomass was, throughout the year, larger than or similar to the planktonic biomass during the peak of the summer bloom, indicating an ability of the colonies to survive in the sediments for extended periods. Abundance of other, non-photosynthetic bacteria varied in the range 3.0–15.5 · 1010 cells g–1 d. w. over the year with minimum values in summer and maximum values in autumn in connection with the sedimentation of theMicrocystis bloom. A substantial part of the non-photosynthetic bacteria, up to circa 40%, was associated with the mucilage of healthyMicrocystis colonies. Bacterial production (3H-thymidine incorporation) appeared to be strongly temperature dependent and less influenced by the seasonal sedimentation pattern. Our data indicate an increasing proportion of non-growing cells in autumn and winter. Biomass-bound phosphorus constituted a significant portion, circa 10%, of the phosphorus content in Lake Vallentunasjön sediments. This pool has normally been overlooked in studies on phosphorus dynamics in lake sediments. Different mechanisms whereby organic phosphorus can be released from the sediments are discussed. 相似文献
10.
Lars Frlin Lennart Balk Malin Celander Sture Bergek Maria Hjelt Christoffer Rappe Cynthia de Wit Bo Jansson 《Marine environmental research》1992,34(1-4)
Recently, analysis of organochlorines in sediment and in pike from Lake Vänern, Sweden, showed a north-south gradient of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). In the present study, good correlations were found between muscle 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) equivalents and liver ethoxyresorufin-O-deethylase (EROD) activities (and P4501A levels) in pike caught at three sampling sites along the north-south gradient in the lake. This comparison between tissue levels of PCDD/PCDF and EROD activity (and P4501A) may indicate that TCDD or structural analogs could be responsible for the observed induction of the pike P450 system. It must, however, be taken into account that the analysed contaminants often do not appear alone but are, rather, accompanied by a range of other substances which may be inducers or antagonists. 相似文献