This report is a contribution to Strategic Environmental Assessment SEA2 conducted by the Department of Trade and Industry (now Department of Energy and Climate Change) and it reviews the distribution and character of pockmarks - shallow seabed depressions - which are common in the area of the North Sea to the north-east of Scotland known as the Fladen Ground. Pockmarks are believed to be produced by the escape of fluids (gas or water, but generally gas in the North Sea) from the seafloor and are found in areas where the seabed sediments are soft, silty clays. Processes of pockmark formation, their geometry, age and distribution, and the sources of gas in the underlying geological strata are discussed. While the great majority of pockmarks are inactive at the present time, a few are observed to be actively seeping gas.
In order to provide a stronger basis upon which the significance of pockmarks within mature oil and gas provinces of the North Sea might be assessed, the Department of Trade and Industry commissioned the acquisition of new data directed towards increasing the scientific understanding of sandbanks and pockmarks as part of the SEA2 process. The survey vessel Kommandor Jack was chartered in April 2001 and, among other operations, conducted high-resolution geophysical surveys of pockmarks in the Fladen Ground. Preliminary results from that operation are included in this report.