International Geologiical Congress - Oslo 2008

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GAH-01 Gas hydrates in oceanic and permafrost environments ? importance for energy, climate and geohazards

 

Seabed fluid structures and relations to gas hydrate reservoirs

 

Berit Oline Hjelstuen, University of Bergen (Norway)
Haflidi Haflidason, University of Bergen (Norway)
 

 

Newly collected TOPAS high-resolution seismic profiles, sediment cores and EM1002 bathymetric data map the upper part of the south Vøring Plateau gas hydrate reservoir in more detail than previously possible. We identify more than 200 pockmarks within a very limited area of this 3000 km2 large gas hydrate region. The seabed depressions have average diameters of ∼100 m and maximum depths of 10 m. Shallow cores indicate that some of these features are active at present. The largest, and most complex, pockmarks are found along the rim of the reservoir. The gas hydrate reservoir and the pockmarks are situated within Plio-Pleistocene well-layered glacimarine and hemipelagic deposits that are overlying a sediment succession dominated by polygonal faults. Glacigenic debris flow units, deposited during shelf-edge glaciations, interfinger the well-laminated sediments on the upper slope. The glacimarine sediments have been delivered to the continental slope by icebergs, suspension fall-out in front of an ice margin and from meltwater plumes released during the disintegration of the Fennoscandian Ice Sheet. The sediment rates may have been as high as 35 m/ky during deposition. Our findings suggest a relation between the occurrence of pockmarks and the gas hydrate reservoir. However, we note that pockmarks do not characterize the entire south Vøring Plateau gas hydrate region; ascribing this to e.g. local variations in sediment characteristics.

 

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