Tectonic evolution and structural styles of the East Shetland Basin

Geometric and stratigraphic evidence indicates that the East Shetland Basin evolved by a rift mechanism similar to that defined in the East African Rift. Arcuate half-grabens of probable Devonian extensional origin are the fundamental structural units. The stratigraphic data suggest episodic footwall movements during the mid- to late Jurassic as well as alternating regional subsidence patterns, i.e. ‘teeter-totter’, against the Horda Platform. The Northern North Sea rift system, which includes the East Shetland Basin, is believed to have opened primarily by orthogonal movement of facing half-grabens rather than by large-scale strike-slip motion between these half-grabens. Both extensional and compressional (or transpressional) features occur in the East Shetland Basin as syn-rift structures. The extensional structures include the well-known tilted fault blocks and relatively undocumented listric normal faults that occur on the crestal and flanking areas of the larger blocks. The principal compressional stress was associated with oblique shearing at the ends of actively extending half-grabens, which created local reverse faults and anticlinal domes. Some rotated horst blocks, e.g. Murchison Field structure, were also created by the transpressional motion. A broad, four-fold E–W structural zonation has been made for the East Shetland Basin and North Viking Graben based on the degree of half-graben development and structural styles.