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Sedimentary Environment Case Studies |
Department of Geology, University of Tromsø, , N-9037 Tromsø, Norway (e-mail: karin.andreassen{at}ig.uit.no)
Former ice-stream activity is shown from industry three-dimensional (3D) seismic data from the south-western Barents Sea. Although designed for deeper targets, the data allow, due to high spatial sample rate and three-dimensional migration techniques, construction of detailed plan view images. The integration of sea-floor geomorphology with stratigraphy documents the importance of glacial processes in the seascape evolution of this area. Fast-flowing ice streams occupying the cross-shelf troughs during the Late Weichselian glaciation caused large-scale erosion, and also left their imprints in the form of mega-scale glacial lineations on the sea floor as indicators of ice-flow direction. Various types of 3D seismic attributes, combined with detailed geomorphology and seismic stratigraphy, are used to investigate the 2–3 km of stratigraphic record that corresponds to over a million years of ice-stream activity. The appearance of mega-scale glacial lineations on various 3D seismic attribute maps indicates, together with other characteristics of ice streams, that they are formed by erosion beneath fast-flowing grounded ice. Bedform records of former ice streams may, however, be related only to the final stages of ice-streaming, immediately prior to shut down. Because we here have preserved up to several hundred metres of sediments between the buried, glacially eroded surfaces, we have the opportunity to study ice-stream imprints and associated processes covering longer time spans than just the last stages. Seismic volumetric attribute maps reveal that megablocks and rafts, often aligned in chains, commonly occur within the till units, implying that glaciotectonic erosion by fast-flowing ice streams was an important process in the transfer of sediments from the continental shelf to the Bjørnøya Trough Mouth Fan and the deep sea during the Plio-Pleistocene glaciations.
