This paper focuses on the Cenozoic evolution of the northern North Sea and surrounding areas, with emphasis on sediment distribution, composition and provenance, as well as on timing, amplitude and wavelength of differential vertical movements. Quantitative information about palaeo-water depth and tectonic vertical movements has been integrated with a seismic stratigraphic framework to better constrain the Cenozoic evolution. The data and modelling results support a probable tectonic control on sediment supply and on the formation of regional unconformities. The sedimentary architecture and breaks are related to tectonic uplift of surrounding clastic source areas, thus the offshore sedimentary record provides the best age constraints on Cenozoic exhumation of the adjacent onshore areas. Tectonic subsidence accelerated in Paleocene time throughout the basin, with uplifted areas to the east and west sourcing prograding wedges, which resulted in large depocentres close to the basin margins. Subsidence rates outpaced sedimentation rates along the basin axis, and water depths in excess of 600 m are indicated. In Eocene times progradation from the East Shetland Platform was dominant and major depocentres were constructed in the Viking Graben area, with deep water along the basin axis. At the Eocene-Oligocene transition, southern Norway and the eastern basin flank became uplifted. The uplift, in combination with prograding units from both the east and west, gave rise to a shallow threshold in the northern North Sea, separating deeper waters to the south and north. The uplift and shallowing continued into Miocene time when a widespread hiatus formed in the northern North Sea, as indicated by biostratigraphic data. The Pliocene basin configuration was dominated by outbuilding of thick clastic wedges from the east and south. Considerable late Cenozoic uplift of the eastern basin flank is documented by the strong angular relationship and tilting of the complete Tertiary package below the Pleistocene unconformity. Cenozoic exhumation is documented on both sides of the North Sea, but the timing is not well constrained. Two major uplift phases in early Paleogene and late Neogene times are related to rifting, magmatism and break-up in the NE Atlantic and isostatic response to glacial erosion, respectively. Additional uplift events may be related to mantle processes and the episodic behaviour of the Iceland plume.
Changes in outbuilding directions and shifts in sediment provenance are key factors for understanding the development of the Cenozoic succession in the central and northern North Sea. By establishing a seismic stratigraphic framework for the Cenozoic succession, and through utilization of velocity data and analyses of sediment compositions, these factors are investigated. Sequence geometries and reflection terminations are identified and related to basin-floor geometry and variations in erosional base level. Mineralogical and geochemical analyses of sediment samples from selected wells are compared with their seismic sequences. Paleogene clastic wedges rich in smectite were built from the East Shetland Platform and probably drained a source area west and northwest of the present North Sea. Outbuilding from southern Norway took place during Late Paleocene-Early Eocene and in Oligocene to mid-Miocene time. In mid-Miocene time outbuilding from the west stopped and subsequently sediments with a high content of feldspar, detrital chlorite and carbonate were deposited from easterly directions in the central and northern North Sea. The seismic velocity of the Cenozoic sediments increases down to a mid-Miocene unconformity, but the velocities of Oligocene and Eocene sediments below are lower and nearly unaffected by burial depth, resulting in a marked velocity inversion. Two tectonic subsidence events, late Eocene-early Oligocene and late Miocene-early Pliocene, have been identified subsequent to general eustatic sea-level lows. These subsidence events cannot be explained by thermal subsidence, and they may have crucial implications for the understanding of hydrocarbon generation, migration and trapping in the Tertiary and deeper stratigraphic levels.
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