Tertiary extensional fault systems on the western margin of the North Sea basin

Major thin-skinned fault systems of Tertiary age, detaching on Permian salt, are present on the platform west of the Central Graben in the Central and Southern North Sea. In plan view the fault systems describe two large arcs which are separated by the Mid North Sea High, partially encircling the West Central Shelf of the Central North Sea and the Silver Pit Basin in the Southern North Sea. The fault trends broadly follow the strike of base salt topography. The geometry of individual faults reflects lateral variation in the role of basement faults and pre-existing Mesozoic thin-skinned extensional structures. Dominant down-to-the-basin fault polarity suggests that the fault systems represent the limit of a gravity-driven slip zone. Extension is largely balanced by down-dip growth of fold structures. Further implications for hydrocarbon exploration include growth of roll-over fold closures adjacent to the fault zones and creation of a tectonic barrier to up-dip fluid migration.