The Cretaceous post-rift basin configuration of the northern North Sea

The present analysis suggests that three stages can be identified in the po st-rift Cretaceous development of the northern North Sea, namely the incipi ent (Ryazanian-latest Albian), the middle (Cenomanian-late Turonian) and th e mature (early Coniacian-early Palaeocene). The transition from syn- to po st-rift configuration was strongly diachronous, suggesting that the thermal state of the system was not homogeneous at the onset of the post-rift stag e. This is supported by observed differences between the early post-rift su bsidence histories of the southern Viking Graben, the Stord Basin and the S ogn Graben. The incipient post-rift stage was characterized by diverse subsidence. The major structural features inherited from the syn-rift basin (e.g. crests of rotated fault blocks, relay ramps and sub-platforms) had a strong influenc e on the basin configuration and, therefore, the sediment distribution. In the middle stage the internal basin relief became gradually drowned by sedi ments. This is typical for basins where sediment supply outpaces or balance s subsidence, as was the case in the northern North Sea. Thus, the influenc e of the syn-rift basin topography become subordinate to the subsidence pat tern which was determined by the crustal thinning profile which, in turn, r elies on thermal contraction and isostatic/elastic response to sediment loa ding. The mature post-rift stage was characterized by the evolution into a wide, saucer-shaped basin where the syn-rift features finally became erased . Since thermal equilibrium was reached at this stage, subsidence ceased, a nd the pattern of basin filling became, to a larger degree, dependent on ex tra-basinal processes. This simple pattern was influenced by the structural inhomogeneity of the basin. This inhomogeneity may have included the grabe n units, in turn related to contrasting geometries of the lithospheric stru cture. The incipient stage of post-rift development was halted by relative uplift/ deceleration of subsidence, locally corresponding to 200 m. This is ascribe d to a hitherto undescribed thermo-tectonic event. The mechanism of this ev ent is not yet known.