Abstract
Extensive patches of shallow gas-charged sediments have previously been documented in the Eastern Skagerrak (the strait between Norway and Denmark). Recently obtained high-resolution side scan sonar and sub-bottom profiler data presented here document several surface and sub-surface features at the border and inside zones of such gas-charged shallow sediments. Three examples are presented and discussed: a low-profile, 3 m-deep pockmark and gas-charged sediments; a low profile, 6 m-deep pockmark associated with a rugged sub-surface reflector; large, up to 25 m deep and 500 m wide pockmarks. From similarities with previously described features it is concluded that the pockmarks are formed by gas eruption and seepage and that the rugged subsurface reflector could possibly represent the upper surface of a diapirically deformed unit of gas-charged plastic clays. Therefore, pockmarks occur preferentially when this rugged surface is close to the seabottom, thus allowing gas-emanation.
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