CoupeFaeroe

North Sea

Central Graben Offshore

This tentative interpretation of a Canvas autotrace of a North Sea regional seismic line depicts the major geologic events characterizing the South Norway Offshore. The Moho discontinuity can be hypothesized at the the bottom of the continental crust. A Paleozoic interval, with a gas generating petroleum sub-system, is visible below the Rotlingende formation, above which were deposited the Permo-Triassic evaporites. An important rifting, characterized by a differential subsidence, took place since Triassic until Upper Jurassic, in which several paroxysm can be recognizing (isopach variations). It is during this period that the organic-rich Kimmeridgian clays were deposited. Since the lengthening of the lithosphere stopped at Upper Jurassic a Cretaceous-Tertiary cratonic basin (North Sea geographic basin) started to develop with an important eastward terrigeneous influx.

This seismic line strongly suggests that in the Norwegian-Danish geographic basin, eastward of the Sørvestlandet high, the Jurassic sediments are absent. Therefore, the conventional generating petroleum sub-systems is unlikely. However, southward of this line, at the level of the Ringkøbing-Fyn high (Danemark Offshore), as shown in next line, the Jurassic sediments are present. A Paleozoic gas generating petroleum sub-system, as well as a Paleozoic-Rotlingende petroleum system are likely in the Norwegian offshore. Such an alternative petroleum system requires pre-Cretaceous traps (pre-migration) below the evaporites and a continuous salt layer (no salt welds).

This tentative geological interpretation of a Canvas autotrace of seismic line shows the Triassic-Jurassic rift-type basins and cratonic basin as well. The Rotlingende sediments can be recognized in the west part of the autotrace, but not in the Ringøbing-Fyn high, which seems be mainly be composed by Precambrian supra-crustal rocks. The rifting Coffee-Soil fault limits the Jurassic sediments. Landward of this fault, the hydrocarbon potential seems very poor or even inexistent, if we assume that migration was mainly vertical. However, in Farsund basin, Jurassic sediments seem to be present (see Page 1B).