Controls on depositional history and architecture of the Oligocene-Miocene succession, northern North Sea Basin

Abstract

The tectonostratigraphic framework of the Oligocene-Miocene succession in the northern North Sea Basin (58 62°N) is closely linked to the large-scale structural evolution of the NW European passive margin. Fairly contemporaneous with the structural doming on the Mid-Norwegian margin uplift activity also affected the Shetland Platform and southern Fennoscandia, including the sedimentary basin of the northern North Sea. This uplift caused a gradual shallowing-upward trend of the northern North Sea Basin, which culminated in severe submarine and possibly also subaerial erosion during middle Miocene, creating a northward increasing stratigraphic break (20 million years in northernmost North Sea), which is visible as a distinct seismic unconformity. Uplift of the East Shetland Platform caused three major phases of sand influx to the basin (1) an early Oligocene phase, resulting in deposition of gravity flow sands in the northern Viking Graben (Statfjord-Tampen area); (2) an early Mioccne phase, resulting in deposition of turbiditic sands (Skade Formation) in southern Viking Graben; and (3) a late Miocene-early Pliocene phase, resulting in deposition of shelfal sands (Utsira Formation). During the latter phase, the northern North Sea Basin formed a relatively shallow marine, shelfal strait between deeper marine settings to the north and south. The Utsira Formation sands accumulated in this narrow strait in a high-energy, possibly tidal-current controlled regime. This chapter also presents an improved lithostratigraphic and chronostratigraphic subdivision of the Oligocene-Miocene including redefinitions of the Skade and Utsira formations. The Oligocene-Miocene succession in the northern North Sea has been subdivided into two megasequences, separated by a seismically distinct unconformity (mid-Miocene break). The age diagnostic Bolboforma assemblages, known from ODP/DSDP boreholes in the North Atlantic and on the Vøring Plateau, have aided in correlation between wells and have been important in resolving the basin history.