HR: 0800h
AN: OS41D-0521    [Abstracts]
TI: 3D Seismic Data From the mid-Norwegian Margin Provide Evidence for Marine Based Ice Sheet Dynamics
AU: * Iversen, H
EM: Henning.Iversen@student.uib.no
AF: University of Bergen, Dept. of Earth Science, Allegt.41, Bergen, 5007 Norway
AU: Nygard, A
EM: Atle.Nygard@geo.uib.no
AF: University of Bergen, Dept. of Earth Science, Allegt.41, Bergen, 5007 Norway
AU: Sejrup, H P
EM: Sejrup@geo.uib.no
AF: University of Bergen, Dept. of Earth Science, Allegt.41, Bergen, 5007 Norway
AU: Haflidason, H
EM: Haflidi.Haflidason@geo.uib.no
AF: University of Bergen, Dept. of Earth Science, Allegt.41, Bergen, 5007 Norway
AB: 3D- seismic exploration data and shallow cores have been used to study glacial deposits along the shelf break/upper continental slope off mid Norway. Glacial fed fans are ubiquitous phenomena on the Norwegian continental slope. Such fans were deposited along the ice front when it reached the shelf break, and are usually found distal to cross-shelf troughs, where glacial debris flows reached hundreds of kilometres down the slope (e.g. c. 500 km on the North Sea Fan). The study area is located in an interfan area, where an up to 250 m thick glacial package (reaching c. 100 km down slope) has previously only been imaged as a seismically transparent wedge, even on high-resolution 2D data. However, the use of seismic attribute analysis on the 3D data volume has made it possible to resolve the internal geometry of the wedge. The attribute analysis reveals a complex internal structure, showing that the wedge consists of coalescing debris flow lobes. The wedge has an average gradient of 0.7 deg, and the bulk of the lobes are from 0.5 to 2.5 km across. Continuous flow lines, which can be followed more than 15 kilometres delineate individual flow bodies. No scarps, blocks, transverse flow elements or indications of brittle behaviour of the sediment are observed. The flow lines show a winding, sinuous pattern and examples of convergence (bottlenecks), which may indicate that the movement of the debris flows was controlled by the underlying topography. These 3D data show that the glacigenic wedge in the interfan area has many of the same characteristics as the glacigenic debris flows on the large fans. However, the run-out distance is much smaller. The core investigations confirm that the material (diamicton) is very similar to that found on the large fans, also with regard to geotechnical properties. This suggests that the rate of sediment delivery to shelf edges is the key difference for explaining the various run-out distances for GDFs in an interfan and fan setting. This again is most likely related to different dynamics of the marine based ice sheet on the shelf in the two areas.
DE: 9335 Europe
DE: 9604 Cenozoic
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
DE: 3094 Instruments and techniques
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting