http://hdl.handle.net/1956/917 Search the Channel search http://bora.uib.no/simple-search http://hdl.handle.net/1956/2333 Title: Ice-sheet dynamics and glacial development of the Norwegian continental margin during the last 3 million years <br/> <br/>Authors: Ottesen, Dag <br/> <br/>Abstract: This thesis is mainly about the dynamics of the palaeo-ice sheets that covered Scandinavia, Barents Sea and Svalbard during the last glaciation. Morphological interpretation of regional and detailed bathymetric data sets on the Norwegian shelf from the North Sea (57°N) to Svalbard (80°N) has elucidated the ice-flow patterns along the western margin of the Scandinavian and Barents/Svalbard ice sheets. About 20 cross-shelf troughs with glacial lineations are interpreted as former pathways for fast-flowing ice streams. The two largest palaeo-ice streams were the Norwegian Channel Ice Stream and Bear Island Ice Stream, each 150-200 km wide at their mouths. Studies of large-scale margin morphology and seismic-reflection profiles have identified large submarine fans at the mouths of several major cross-shelf troughs. Improved knowledge of the regional development of the margin, and detailed morphological maps of the buried palaeo-surfaces, show that similar large-scale glacial processes have been active in a substantial part of the Late Pliocene/Pleistocene (c. last 3 million years). Interpretation of a large seismic data base has made it possible to map the whole Naust Formation, which comprises sediments deposited on the mid-Norwegian margin during the last 3 million years. During this period, large quantities of glacially derived material were transported westward from the Norwegian mainland and the inner parts of the shelf, and deposited mainly as prograding sediment wedges into a basin of intermediate depth offshore of Mid Norway. The deposits are more than 1000 m thick over an extensive area, and the shelf edge migrated up to 150 km westwards. Very-high-resolution bathymetric data has made it possible to study sedimentary processes related to recently surging glaciers on Svalbard (the last few hundred years). The data sets also show that mega-scale glacial lineations not only can form beneath large ice streams, but are also produced over a few years beneath surging tidewater glaciers lying on deforming sedimentary beds. Thu, 28 Jun 2007 22:58:59 GMT http://hdl.handle.net/1956/2270 Title: Numerical simulation of turbidity currents: a new perspective for small- and large-scale sedimentological experiments <br/> <br/>Authors: Heimsund, Snorre <br/> <br/>Abstract: Turbidity currents are a variety of subaqueous sediment-gravity flows, in which the suspension of sediment by water turbulence produces a water-sediment mixture that is denser than the ambient water and hence flows due to gravity along a topographic gradient. This type of sediment gravity flow is the most important mechanism for the dispersal and deposition of sand on deep-sea floors, as well as on the underwater slopes of many deltas and lakes. The hydrodynamics of turbidity currents are difficult to study in the natural environments, whereas laboratory experiments are limited to small-scale flows, time-consuming and not necessarily easier when it comes to the measuring of flow properties and establishing of the relationships between the turbulent flow structure and the transport and deposition of sediment. Mathematical models of turbidity current, integrated by computational fluid dynamics (CFD) and realized as numerical simulations, can be used to obviate these difficulties, and also to upscale laboratory datasets and to integrate the data from nature and experiments. The concept CFD refers to the numerical solution, by computational methods, of the governing equations describing fluid flow: the set of Navier-Stokes equations and the multi-phase fluid dynamics. CFD is widely used in the engineering branches of fluid mechanics, but is a relatively new numerical approach in the field of sedimentological research. In the present study, a three-dimensional model has been constructed by using the CFD software Flow-3D™ to simulate the flow of turbidity currents, including their internal hydraulic characteristics as well as sediment erosion and deposition. The Flow-3D™ model employs finite difference and finite volume methods and the turbidity current is being simulated by a range of physical models: 1) the turbulent flow structure is simulated by a turbulence model based on renormalization group theory that employs statistical methods to calculate turbulence quantities; 2) the water-sediment mixture is calculated by a drift-flux technique that describes the relative flow of two miscible fluids with different densities; 3) interactions between the continuous fluid and the dispersed mass particles are calculated by the particle model; and 4) the erosion and deposition of sediment are calculated by the sediment scour model. Simulations of small-scale turbidity currents imitating particular laboratory flows have shown that the results of Flow-3D™ are realistic and reliable. Similar series of flow simulations have been used further: 1) to display in a flow-parallel axial section the main hydraulic characteristics (bulk density, shear-strain rate, dynamic viscosity, velocity magnitude and its x-y-z components) of a channelconfined current; 2) to display of the shear stress, sediment concentration and velocity magnitude for several ‘probing stations’ in a channel-confined current expanding abruptly on an open-space flat floor; 3) to study the responses of the confined and unconfined parts of a current (in terms of its velocity magnitude, shear stress and sediment concentration) to changes in such principal controlling parameters as the channel slope angle, sediment grain size, floor roughness and initial sediment concentration; 4) to display sediment grain-size segregation in a current (using a flow run with polysized sediment suspension); 5) to display the velocity time series for a surge-type and a sustained turbidity current; and 6) to show the responses of turbidity current to various obstacles and to a hydraulic jump at the channel outlet. Two large-scale simulations of ‘real-life’ turbidity currents have been performed, one imitating modern flow events in the Soquel and Monterey canyons, offshore California, and another pertaining to the deposition of the Egga reservoir unit in the Ormen Lange field, Mid-Norway Continental Shelf. The present study has evaluated Flow-3D™ as a possible means of simulating hydrodynamic behaviour of turbidity currents. The comparison of numerical and flume data indicates that the CFDbased Flow-3D™ models can give realistic results and serve as an attractive alternative to laboratory flume experiments. The use of a CFD software, such as the Flow-3D™, has several great advantages: 1) it allows a much wider range of flow parameters to be determined and continuously monitored with a relatively high accuracy; 2) it permits the response and relative importance of the individual flow parameters to be assessed with respect to changes in the initial conditions; 3) it allows turbidity currents to be up-scaled to natural conditions; and 4) it provides an unprecedented insight in the detailed hydrodynamic aspects of turbidity current. The study indicates that our understanding of turbidites and their variability can be significantly improved by this type of experimental research. Sun, 29 Oct 2006 22:58:59 GMT http://hdl.handle.net/1956/2015 Title: Deep-water depositional systems of the Norwegian Sea : understanding the system evolution, depositional geometries and reservoir quality from subsurface data and field outcrops <br/> <br/>Authors: Lien, Trond Thu, 19 Oct 2006 22:58:59 GMT http://hdl.handle.net/1956/2010 Title: Paleoceanography and paleoclimate in the Nordic Seas and the northern North Atlantic during the last 22 000 years <br/> <br/>Authors: Meland, Marius Yddal <br/> <br/>Abstract: The paleoceanography of the Nordic Seas and the northern North Atlantic during glacial and deglacial times was studied, using oxygen isotopes and Mg/Ca of foraminifera. The specific objectives are listed below: 1) Sea surface temperatures (SST) during the Last Glacial Maximum (LGM, ∼20 000 years ago) were reconstructed, using oxygen isotopes of the planktonic foraminifer Neogloboquadrina pachyderma (sinistral). 2) The LGM climate (air temperatures, precipitation/moisture, air pressure, wind systems) was simulated, using the SSTs produced under Objective 1 as boundary conditions. 3) Mg/Ca ratios of N. pachyderma (sin.) were tested to see if they could be used to make surface/subsurface temperature estimates in the Nordic Seas for previous times. 4) Water mass exchanges between the North Atlantic and the Nordic Seas through the period 22 000 - 6000 years ago were studied. This period covers the LGM, the last deglaciation and the recent interglacial (Holocene). Benthic oxygen isotopes were used as the main proxy, supported by benthic carbon isotopes and planktonic oxygen isotopes. Thu, 31 Aug 2006 22:58:59 GMT http://hdl.handle.net/1956/1806 Title: Effects of upscaling and interpolation on log data <br/> <br/>Authors: Bakke, Roger Fri, 29 Oct 1999 22:58:59 GMT http://hdl.handle.net/1956/1805 Title: Inversjon av seismiske data mot akustisk impedans og bergartsparametre <br/> <br/>Authors: Myhren, Bjarte Fri, 29 Oct 1999 22:58:59 GMT http://hdl.handle.net/1956/1804 Title: The sedimentation pattern of the last deglaciation and postglacial phase in a high-arctic valley: Endalen, Spitsbergen <br/> <br/>Authors: Soltvedt, Stian <br/> <br/>Abstract: The present study, focused in the valley-side gravel fans in the eastern part of Endalen and the adjoining side-slope of Adventdalen, has contributed to an understanding of the spatial pattern of the late Weichselian deglaciation and associated meltwater drainage in a 3rd-order and a 2nd-order valley and adjacent mountain plateau in central Spitsbergen, Norwegian high-Arctic. The author’s fieldwork in 1998 was focused on the following main topics: (1) the mapping and chronology of postglacial sediment accumulations, with special emphasis on the development history and depositional processes of the valley-side gravel fans; (2) the snow-cover conditions on the valley-side slopes during the winter to autumn season 1998, including comparative photographic documentation and fixed-point snow thickness measurements; and (3) the assessment of the intensity, routes and controlling factors of the downslope transfer of sediment and water, including the recognition and spatial pattern of meltwater palaeoflow scours and their significance for the reconstruction of the ice-sheet retreat. The analysis of infrared aerial photographs has proved to be very useful in deciphering the areal pattern of meltwater palaeodrainage and in the recognition of other glacial/postglacial geomorphic features. Arrays of surficial palaeochannels are recognizable on the eastern plateau of Endalen, trending NW and lacking any obvious water catchment today. These scours are attributed to the meltwater runoff during the early Holocene deglaciation. The morphological mapping revealed also relict late-glacial deposits in the form of a lateral moraine and several raised beach terraces near the mouth of Endalen, but no preserved glacigenic diamicton deposits have been recognized on the adjacent eastern plateau. Erratic cobbles and boulders have been found on western plateau, directly outside the Endalen drainage basin, which indicates that the mountain plateaux were covered by the glacier. Some long-transport erratics, derived probably from the eastern part of Spitsbergen, have also been identified in Endalen and on the valley’s eastern slope. Based on the aerial photographs and direct field observations, a tentative spatial model has been suggested for the deglaciation of the Adventdalen area. The valley-side gravel fans whose formation involved meltwater flow from the plateau are larger, associated with well-incised ravines and show two stories of deposits recognizable in geomorphic terms: a broad mound of older, vegetated base-of-slope deposits (alluvial fan), distinguished as sedimentation stage I, and a smaller, steeper accumulation of relatively fresh younger deposits (colluvial fan) superimposed onto the upper/apical part of the former and distinguished as sedimentation stages II and III. The three stages of deposition are interpreted as: (I) an early Holocene, early postglacial stage dominated by the meltwater runoff from the plateaux and coeval high-viscosity debrisflows on the mountain slopes between the ravines; (II) a middle Holocene stage dominated by rockfall processes and minor debrisflows; and (III) the late Holocene stage dominated by the more mobile, watery or slush-laden debrisflows. The low-viscosity debrisflows of stage III have commonly caused strong incision in the fan apex and upper segment, with channels up to a few metres deep and the associated intersection-point deposits making the fan prograde in a “telescoping” style and aggrade in the lower segment. The tripartite stratigraphy of the valley-side fans is thought to reflect the Holocene regional climatic changes. The snow cover in the study area is generally sparse, due to the low precipitation in the Arctic desert, but the predominance of strong and variable winds renders them a key agent controlling the thickness distribution and local excessive accumulation of snow in Spitsbergen. In Endalen, the winter winds are capable of filling ravines with several metres of snow and forming large snow cornices, although no snow avalanches (nor any other active slope-waste processes) have been observed on the valley slopes during the weekly visits in 1998. Slope-waste processes are infrequent and highly episodic. Most of the snow cover seems to disappear due to the processes of sublimation and gradual melting, with the main phase of melting in the early June. The meltwater runoff from the mountain plateau is very limited and incapable of removing large amounts of debris from the ravines, except for the fine-grained sediment, rarely coarser than sand or perhaps granule to fine-pebble gravel. However, the percolating water almost certainly has the capacity to infiltrate the coarse, ravine-entrapped gravel with fine sediment, and this watery matrix might then lubricate the gravel mass and turn it into a debrisflow. The presence of slush in the ravines may have a similar lubricating effect on the cobbly to bouldery rockfall gravel that tends to accumulate in the steep bedrock ravine. Fri, 29 Oct 1999 22:58:59 GMT http://hdl.handle.net/1956/1690 Title: The Diagenesis and porosity of the mixed deposits of the Azagador Member (U. Miocene) in the Turre Area, Almeria, Spain <br/> <br/>Authors: Enge, Håvard H. Mon, 29 Oct 2001 22:58:59 GMT