Abstract: Salt Tectonics in the North Sea

Michael Coward, Simon Stewart

The North Sea differs from other salt basins in that it forms a closed system. Section construction and balancing through the carapace of the North Sea needs to take into account thin-skinned and thick skinned extensions and contractional tectonics. The North Sea salt formed during Permian times in two large oval shaped basins separated by the Mid-North Sea High. Subsequent salt tectonics are governed partially by local graben structure but more importantly by regional uplift and subsidence. They occurred as a result of:

1. Rifting initiated during the Triassic - allowing reactive and locally passive diapirs to develop in the post-salt carapace. The grabens in the carapace are generally offset from rifts in the basement and occur at the edge of the zone of subsidence, at the basin margin in the Southern Gas basin or at the edges of rift-flank uplift associated with extension in the Central Graben.

2. Gravity gliding of the carapace away from zones of rift flank uplift associated with Late Jurassic-Early Cretaceous extension - and also into half-graben developed by late Jurassic and Early cretaceous rifting. This caused reactive graben to develop on the flanks of the uplifts and asymmetric compressional pillows to develop downslope.

3. Gravity gliding of the carapace associated with tilting of the North Sea during thermal subsidence in the Cretaceous-Tertiary, enhanced by pulses of tectonic inversion along the flanks of the North Sea during the Late Cretaceous and Early Tertiary. Where the compressional pillows have been eroded sufficiently, the salt breaks through the thinned cover to produce a new active and then passive diapir which may drain the pillow and produce a rim syncline. Locally the diapirs developed during early gliding phases are compressed during later phases.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France