Abstract
That a major rift system lies beneath the North Sea is now widely accepted. A chain of graben basins extends for more than 1,000 mi (1,600 km) from the northern North Sea to The Netherlands and possibly into the Rhine rift system. Fault-bounded basins beneath the continental shelf west of Norway and in eastern Greenland are a probable northward continuation of the rift system. The Viking graben, central graben, and North Netherlands graben have been explored intensively during the last decade in the search for oil and gas.
The North Sea grabens have a history of active subsidence, by both faulting and downwarp, from the Late Permian to the Early Cretaceous. Some evidence from surrounding onshore areas suggests that rifting may have begun as early as the Devonian. About the middle of the Cretaceous, rifting was replaced by a regime of regional subsidence which continued throughout the Tertiary. Major oil and gas reserves have been established in Jurassic sandstones and in Tertiary limestones and sandstones, in tilted fault blocks, anticlinal drape structures, and salt-generated anticlines.
It is suggested that the tensional rifting was closely associated with early attempts at opening of the North Atlantic Ocean. Rifting essentially ceased in the North Sea in the middle Cretaceous when active opening of the North Atlantic began west of the Rockall-Hatton Bank. There is no evidence for actual plate separation across the North Sea rifts but it is considered possible that plume-generated uplift and crustal thinning predated the graben collapse.
