Abstract for poster presentation at 33rd Annual Arctic Workshop April 3-5, 2003. Tromsø, Norway
3-D seismic data reveal palaeo-ice flow pattern from glacigenic sediments, southwestern Barents Sea
Rafaelsen, B.1, Andreassen, K.1, Kuilman, L.W.2, Lebesbye, E.1 & Hogstad, K3
AFFILIATION(S):
1 Department of Geology, University of Tromsø, 9037 Tromsø (Norway)
2 Norsk Hydro ASA, 0246 Oslo (Norway)
3 Norsk Hydro ASA, 9480 Harstad (Norway)
The section of glacigenic sediments between the upper regional unconformity (URU) and the sea floor, up to 120 m of sediment, have been interpreted from industry 3-D seismic data. The study area, covering totally 2870 km2, is located in the south-western Barents Sea. Our 3-D seismic data have a good vertical and horizontal resolution, thus providing detailed maps of palaeo surfaces, revealing lineations with a relief of down to 2.5 m. The interpreted 3-D seismic data sets suggest a more complex glacial history than previously described.
One of the seismic cubes reveals a ridge complex on the seafloor, being 12 km long, 500 m wide, 24 m high, and steeper in the west than in the east. The ridge complex is interpreted to be a glaciotectonic ridge formed sub- or pro-glacially, thus indicating that the direction of ice flow was from west towards east. Proximal to the ridge complex a depressed area, being topographically lower then the rest of the sea floor, may suggest from where the sediments in the ridge complex originate.
In the glacigenic section, imbricated structures appearing crescentic in map view, occur. They consist of 300-700 m long and around 300 m wide sediment sheets that are stacked upon one another for distances of 0.5 to 5 km. In vertical cross-sections these features have the appearance of imbricated trust sheets which downwards seem to sole out along a basal decollement zone. Some of them even reach the sea floor, while other go as deep as down to the URU. These imbricated crescentic thrust sheets are interpreted to be of glaciotectonic origin, indicating a direction of ice flow towards east and west. 146 imbricated structures have been mapped in the study area.
Several generations of large-scale lineations, observed on four different palaeo-surfaces are interpreted to reflect ice flow patterns of palaeo glaciers. Earlier studies in nearby areas suggest an ice flow direction in the Bjørnøyrenna towards west during the last glacial maximum. The main pattern of the lineations in our data set trends N-S on all four palaeo-surfaces, suggesting a dominant ice flow direction from south to north across the Barents shelf at least four times during the last 0.8 Ma. Our data indicate that if the flow of grounded ice in Bjørnøyrenna has been towards west, there may have been a convergence-zone in the southern part of Bjørnøyrenna. A second possibility is that the grooves in our data set were formed while the ice was retreating. In the latter case the N-S-trending grooves in our data-set may have been formed while Bjørnøyrenna was ice-free and acted as a major calving bay for the ice moving from south towards north. This suggests that evidence from the ice advances my have been obscured during the retreat of the ice. Thirdly, the grounded ice covering the south-western Barents Sea may have had a dominant direction of ice flow towards north or south.