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| Titel |
Subglacial processes based on 3D seismic data |
| VerfasserIn |
Karin Andreassen, Monica Winsborrow |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250034422
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| Zusammenfassung |
| The beds of former ice sheets and the internal structure of underlying tills can provide detailed information about subglacial processes. Here we present observations from three-dimensional (3D) seismic data, revealing buried beds of the former Barents Sea Ice Sheet (BSIS) from several glaciations. Sediments of continental shelf breaks and upper slopes are also imaged. The BSIS, located at the northern flank of the former Eurasian ice sheets, offers a good geological analogue to the contemporary West Antarctic Ice Sheet.
The 3D study area is located at the outer, southern flank of Bjørnøyrenna (the Bear Island Trough), which acted as a pathway for the Bjørnøyrenna Ice Stream, that transported large amounts of ice and sediments to the SW Barents Sea Margin. This margin has experienced subsidence since Early Cretaceous, providing accommodation space for the 3-4 km of Pleistocene glacigenic sediments of the Bjørnøya Trough Mouth Fan, that represent an archive corresponding to over two million years of glacial activity.
The data document that the former Bjørnøyrenna Ice Stream periodically since the start of shelf edge glaciation 1.5 million years ago has brought large amounts of sediment blocks and rafts to the SW Barents Sea shelf break and upper continental slope, where they accumulated as till deltas. The data indicate that the sediments were incorporated into the ice stream by brittle deformation during compressive ice flow. Overlying mega-scale glacial lineations and pull-apart of sediment blocks indicate extensional flow. Till stiffening, due to subglacial freezing and ice-stream slowdown or quiescence, is the favoured mechanism for creating these switches in sub-ice stream conditions. The observed patterns of geomorphic features indicate that a common ice-stream behaviour through several glaciations was alternations between 1) ice-stream slowdown or quiescence with freezing-on of subglacial sediments and 2) fast ice flow with transportation of frozen-on sediments. In more ice-distal, continental slope- or deep sea settings, the signature of these sub-ice stream thermal changes (and high sediment delivery to the shelf break) is inferred to be increased mass movement activity and pulses of ice rafted debris (IRD), which have implications for interpretation of IRD records. |
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