Pockmarks in the inner Oslofjord,Norway |
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| Authors: | Karen E Webb Øyvind Hammer Aivo Lepland John S Gray |
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| Institution: | (1) Physics of Geological Processes, University of Oslo, P.O. Box 1048, Blindern, 0316 Oslo, Norway;(2) Norwegian Geological Survey, 7491 Trondheim, Norway;(3) Institute of Biology, University of Oslo, Oslo, Norway |
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| Abstract: | Multibeam bathymetric surveys of the Inner Oslofjord, Norway have revealed a high density of pockmarks in the 179-km2 inner fjord area, which contains over 500 pockmarks of varying size, typically 20–50 m in diameter and 2–10 m deep. These
pockmarks have been investigated with a variety of techniques, including acoustic subbottom profiling, sedimentological and
geochemical analyses of cores, remotely operated vehicle observation, and morphometry. Both the distribution and shapes of
the pockmarks suggest that they are related to structures in the bedrock underlying relatively thin (<50 m) unconsolidated
glacial and postglacial sediments. The data provide no direct indication of a particular mode of pockmark formation, but release
of large amounts of biogenic, shallow methane seems unlikely. Several lines of evidence point to a continuous process of pockmark
formation followed by inactivity, with some pockmarks recently active whereas others have been inactive for a considerable
time. Some pockmarks are characterised by coarse sediment in their centres. The density, variety and easy access make this
pockmark field an ideal model area for pockmark research.
John S. Gray is deceased. |
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