Extended abstract

T. Eidvin, F. Riis, E. S. Rasmussen & Y. Rundberg, 2013. New layout 2021

Regional seismic interpretation indicates that offshore West and Mid Norway and along the western Barents Sea margin, the Paleocene-Eocene sediment progradation was terminated in the period from the latest Eocene to the earliest Oligocene, and the Eocene clinoforms were onlapped by Oligocene shales.

This occurred at the same time as there was a shift in the drainage divide of West Norway which caused transport of Oligocene coarser clastics southwards towards the Norwegian-Danish Basin. From now on prograding slope/deltaic systems developed in the Norwegian-Danish Basin (Vade Formation and Dufa Member). In the northern North Sea, gravity-flow sand was sourced from the Shetland Platform and to a lesser degree from Fennoscandia. Along the inner continental shelf of the Norwegian Sea, a pronounced out-building of coastal plains and deltas started (Molo Formation). Coarse clastic sediments were deposited in northwestern Svalbard, while argillaceous sedimentation prevailed elsewhere, except for the deep-water Norwegian Sea where mainly siliceous ooze accumulated. On the outer Vøring Plateou contourite growth prevailed. The climate was probably cold temperate during the Early to early Late Oligocene and warm temperate to subtropical during the latter part of Late Oligocene.

During Early Miocene, global climatic variations and major sea-level changes combined with uplift of the southern part of the Fennoscandian Shield led to increased sediment transport from the north (present-day Finland, Sweden and particularly Norway) towards present-day Denmark. Deltas (Ribe Group) covered large parts of the present-day Jutland area. In the western part of the Viking Graben in the North Sea, sand-rich gravity deposits of the Skade Formation were sourced from the Shetland Platform. To the east, in the central part of the basin north of 60ºN and in the Central Graben, fine-grained sedimentation occurred. The out-building of the Molo Formation along the inner Norwegian Sea continental shelf continued durin the Early Miocene. To the west, thin successions of fine-grained deposits are recorded on the Trøndelag Platform, and mainly pelagic ooze was laid down in the Norwegian Sea (Brygge Formation).

The uplift culminated at the Early to Middle Miocene transition, and the deposition of the Skade Formation sands was followed by a large fall in relative sea-level. In the Norwegian Sea, major compressional features, e.g. the Helland Hansen Arch, were formed. In the southern North Sea and Norwegian-Danish Basin subsidence continued. During the Middle Miocene, mainly fine-grained sediments were deposited in most parts of the Viking and Central Graben, and in parts of the Trøndelag Platform on the Norwegian Sea continental shelf. However, in the western part of the Viking Graben deposition of sand still prevailed. The southern North Sea and the Norwegian-Danish Basin subsided and record a complete Middle to early Late Miocene succession. In the southern Viking and Central Graben hiatuses are minor or absent. A local hiatus is present in the Middle Miocene in well 2/4-C-11(Ekofisk Field) probably due to salt tectonics and polygonal faulting. Pelagic sedimentation and contourite growth continued uninterrupted in most of the Norwegian Sea and continued into the Late Miocene and Early Pliocene (Kai Formation). However, hiatuses are probably present on large dome structures. The Barents Sea margin was also uplifted, and a hiatus is recorded below the Middle Miocene in the Sørvestnaget Basin. In the Vestbakken Volcanic Province there is a break between the Upper Pliocene and Lower Miocene. The climate was probably warmtemperate during the Early Miocene and culminated with a subtropical climate in the early Middle Miocene.

In the Late Miocene, a marked relief of the Fennoscandian Shield, accompanied by continued uplift, a colder climate and a low global sea-level, resulted in a continued and pronounced out-building of the coastal plains and deltas along the inner Norwegian Sea continental shelf (Molo Formation). During the same period the northern North Sea formed a narrow seaway between deeper water in the Møre Basin and the central North Sea. The strait received a large amount of coarse clastics (Utsira Formation), mainly from the East Shetland Platform in the west but also from the Sognefjorden area in the east. Offshore West Norway farther to the south, only thin and shaly sections are recorded. Mainly fine-grained deposition continued towards Denmark and the Norwegian Sea, probably using the drainage systems which were established in the Oligocene and Early Miocene. This situation lasted through the Early Pliocene when the global temperature and sea level temporarily rose.

Investigation of the large sediment wedge off the Scoresby Sund fjord system has shown that the build-up of a substantial continental ice sheet on Greenland started in the Late Miocene at approximately 7.5 Ma.