Northern North Sea basin
[1] Total recoverable reserves found to date, including adjacent land areas, amount to over 100 billion barrels of oil and natural gas.
[1] The northern North Sea Paleorift system, including the Viking and Sogn graben, is an approximately 150–200 km wide zone of extended upper crust with preserved strata from pre-Triassic to Tertiary.
Rotational movements on major fault zones bounding the northern Viking Graben commenced in the latest Bajocian-earliest Bathonian and ceased in the earliest Ryazanian.
[1] The Cretaceous-early Cenozoic succession in the northern North Sea largely represents post-rift infill, resulting from subsidence in response to lithospheric cooling following the late Jurassic-early Cretaceous stretching event.
The architecture and signature of the sediment infill in the northern North Sea can be discussed in the context of three distinct evolutionary stages of rift basin development separated by key geologic unconformities.
The combined thermal and elastic/isostatic response of the lithosphere to extension controls the crustal architecture and thereby the geometry of sedimentary basins, including those of the northern North Sea.
[3] Proto-rift basins are typically saucer-shaped, slightly deepening towards the future graben axis, which can lead to large axial sediment transport systems.
[8] As domal uplift related to incipient rifting is commonly associated with subsidence in its vicinity, erosional products tend to accumulate in associated depositional basins that may be a proto-rift, as with the Brent Delta system.
[3] The subsidence is counteracted by upwelling of the asthenosphere into the space created by the mechanical stretching and thermal upward displacement of the asthenosphere-lithosphere boundary, causing uplift of the rift zone.
The location and number of half grabens are influenced by the position of the main faults and the width of the rift zone, which depends on the rheology, crustal thickness and stretching factors.
[3] Half-graben and wedge-shaped infill geometries characterize both the Permo-Triassic and late Jurassic stretching events in the northern North Sea, most prominently in the area southwest of the Brent Field.
More evidence of progressive rift climax with divergent stratal patterns occurs across the major eastern boundary fault of the East Shetland Platform.
Several rotational maxima led to the deposition of wedge-shaped units downflank in hanging wall positions, in response to footwall crestal uplift and erosion.
[10] The Visund fault block and the Oseberg-Brage infill are examples from marine half-grabens which are near the central or axial zones of the northern North Sea rift complex, far from the main hinterland areas and show deepening upward trends into basinal shales.
[3] The early Cretaceous post-rift phase in the northern North Sea was characterized by slow subsidence, with much of the sedimentation accommodated by the infilling of previous rift bathymetry.
The gradual passage from continental coarse clastic sediments into shallow marine shales in the middle Triassic-lower Jurassic post-rift succession in the northern North Sea serves as a good example of such a model.
