Glacial dynamics and fluid flow processes in Bjørnøyrenna and the Loppa High area, SW Barents Sea

Abstract

During the Late Weichselian glaciation, the Bjørnøyrenna ice stream was the main outlet of the Barents Sea Ice Sheet. In this thesis, a 3D seismic dataset from the Loppa High, located in the main ice stream trunk, has been used to study the glacial sediment package, revealing details on pastglacial dynamics, fluid flow processes and gas hydrate formation. Three seismic horizons have been interpreted: the seabed, an intra Quaternary horizon and the Upper Regional Unconformity (URU), which corresponds to the base of the Quaternary glacial sediment package. On the intra Quaternary horizon, megascale glacial lineations (MSGL) and a glacitectonic line of depressions are observed, 10 km apart. The MSGL are suggested to indicate fast flowing ice and a warm based bed while the glacitectonic line of depressions indicate cold base and slow ice flow velocities. Seismic indications of fluid flow and gas hydrate formation are associated with the glacitectonic line of depressions. We therefore suggest that gas hydrate formation promoted the freeze-on of subglacial material to the base of the ice stream, triggering glacitectonic erosion, excavating the line of depressions. On URU, bedrock ridges and a subglacial meltwater channel are interpreted. The meltwater channel follows the outline of the Bjørnøyrenna Fault Complex which is suggested be a weakness zone prone to glacial and meltwater erosion. The subglacial meltwater channel is proposed to have accelerated the flow of the overlying ice due to lower basal drag. The surrounding areas on URU consist of bedrock ridges. Their formation is attributed to the differential resistance to glacial erosion of alternating soft and hard interbeds in the underlying bedrock. It is suggested that this created a rough subglacial bed, and this, together with the fact that no landforms indicative of fast flowing ice are observed associated with these bedrock ridges, is consistent with slower ice flow velocities in this area compared to within the meltwater channel.