Geological setting

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

The Oligocene and Miocene sediments investigated for this publication are sampled from wells, boreholes and outcrops which belong to six different provinces along the North Atlantic Margin.

Prior to the Oligocene, the geological history of these provinces was influenced by several processes related to Paleocene and Eocene break-up, volcanism, rifting and strike-slip movements in the Atlantic domain. A significant change in the plate tectonic setting took place at the time of magnetic anomaly 13 when the rifting and spreading activity at the Kolbeinsey Ridge west of Jan Mayen was initiated. This event corresponds approximate to the Eocene-Oligocene boundary, e.g. Faleide et al. (1996) and Eidvin et al. (1998b). Following this plate tectonic rearrangement, strike-slip tectonic activity along the western Barents Sea and Spitsbergen margin ceased and gave way to sea-floor spreading in the Norwegian-Greenland Sea. In all the provinces described, deposition of Oligocene and Miocene sediments took place in a tectonically quiet passive-margin setting, although an event of Mid Miocene compression is recorded in the Norwegian Sea and southern North Sea. The geometries of the basins, the uplift of the hinterlands and the local climate were constrained by pre-Oligocene events. Several pulses of coarse clastic sedimentation are found in the Oligocene-Miocene sedimentary record. Such events can be interpreted as responses to tectonic uplift of the Scandinavian hinterland or the Shetland Platform, or, alternatively, as non-tectonic processes such as sedimentary progradation, rearrangement by ocean current circulation (Laberg et al. 2005b) as well as eustatic and/or climatic changes which thus influenced the clastic input to the basins. Good correlation between the wells in the region is important in order to understand the geological history, interpret the paleogeography and to map the distribution of economically important reservoir sands in the region.

East Greenland – Scoresby Sund.

The Scoresby Sund Fan forms the largest accumulation of Neogene sediments along the entire East Greenland Margin (Profile P14 and ODP Site 987). It has a slope of about 2º beyond the shelf break with the total sediment volume estimated at 30 000 ± 10 000 km3 (Dowdeswell et al. 1998, Butt et al. 2001). The fan occupies the Outer Liverpool Land Basin and is located at the mouth of the large drainage system of Scoresby Sund, which is bounded to the south by the Paleocene volcanic province of East Greenland and to the north by the Mesozoic sedimentary province of Liverpool Land. The hinterland area was strongly uplifted in the Cenozoic, and the stratigraphy of the fan is of interest for the timing and reconstruction of the geological development of the region.

The Liverpool Land Basin

contains an approximately 10 km-thick sediment pile overlying oceanic/volcanic basement (Larsen 1990, Butt et al. 2001) and is located to the north of the Blosseville Kyst Basin in the shelf region in the vicinity of the Scoresby Sund Fjord complex. The Iceland Plateau and the Kolbeinsey Ridge form the eastern boundary of the basin. The evolution of the area has been strongly influenced by Cenozoic tectonic events, which principally consist of an early phase of rift basin formation and a later phase of sea-floor spreading (Larsen 1990, Butt et al. 2001).

The Forlandssundet basin.

In Forlandssundet, West Spitsbergen, Cenozoic sediments are infilling an elongate, fault-bounded, basinal structure within the hinterland of the Spitsbergen orogen (see Map 2 and Forlandsundet). Offshore seismic data show that the basin belongs to a coast-parallel structure, about 30 km wide and 300 km long (Sigmond 1992). The Cenozoic regional deformation of Svalbard and formation of the West Spitsbergen Orogen is related to the opening of the Norwegian-Greenland Sea and dextral motion between Greenland and Svalbard in the Paleocene and Eocene (Gabrielsen et al. 1992, Maher et al. 1997, Braathen et al. 1999, Bergh et al. 1999). The main transpressive/compressive tectonism of the orogen affected the Paleocene and Eocene sedimentary rocks outcropping in the thrust/fold belt in central parts of West Spitsbergen, whereas the sediments of Forlandsundet were deposited in a different tectonic setting where both normal faulting and strike-slip faulting prevailed.

In the literature, the age of the sedimentary fill of the Forlandsundet basin, based on foraminiferal and strontium isotope studies, has been considered to be Oligocene by Feyling-Hanssen & Ulleberg (1984) and Eidvin et al. (1998b), whereas Manum & Throndsen (1986) interpreted the sedimentation as Eocene based on palynological studies. Given an Eocene age for part of the fill, the basin would have formed partly coevally with contractional deformation in the thrust-belt to the east, thus indicating a complex regional strain partitioning. On the other hand, if all of the basin fill is Oligocene, the basin itself could post-date the West Spitsbergen orogeny. Consequently, a more reliable age determination of these sediments is important for the reconstruction of the last phases of the formation of the orogen and correlation with the plate tectonic events.

The Western Barents Sea margin.

The present continental margin of the western Barents Sea and Svalbard (see Map 2, Profile P15 and Profile P15 map) extends for about 1000 km in a broadly north-northwesterly direction. It comprises three major structural segments, including a southern, sheared margin along the Senja Fracture Zone, a central volcanic rift segment (Vestbakken Volcanic Province), and a northern sheared and subsequently rifted margin along the Hornsund Fault (Ryseth et al. 2003). The evolution of the margin is closely linked to the opening of the Norwegian-Greenland Sea. In the Paleocene-Eocene, transcurrent movements prevailed, with the Vestbakken Volcanic Province opening as a pull-apart basin. From the Oligocene onwards, oceanic crust developed along the entire margin between Norway and Svalbard, leading to subsidence of a passive margin. Small amounts of Oligocene and Miocene sediments accumulated in local basins east of the main boundary fault between continental and oceanic crust. The biostratigraphic and Sr-isotope analyses of these sediments are important for the timing of the formation of these basins and their correlation with the main plate tectonic events. Post-Eocene sediments are generally not preserved on the Barents Sea shelf. Later, in the Pliocene to Pleistocene, a very thick, Neogene, sedimentary wedge accumulated as a result of glacial processes acting in Svalbard and on the Barents Sea shelf (Faleide et al. 1996, Ryseth et al. 2003 and Laberg et al. 2012).

The Norwegian Sea and its continental shelf

Represent different structural settings (Fig. 6). The Møre and Vøring basins are characterised by exceptionally thick Cretaceous successions and a complex Cretaceous and Cenozoic tectonic history (Blystad et al. 1995, Brekke 2000). The Utgard High forms the eastern flank of the Late Cretaceous Någrind Syncline, and the drilled wells reveal a complex and condensed Paleogene and a very thick post-Cenomanian Cretaceous succession. In Oligocene to Early Pliocene times, the Møre and Vøring Basins were located in a distal position relative to sediment supply from Scandinavia, and biogenic ooze makes up a significant part of the succession. Large compressional structures were formed during Mid Miocene tectonism. In the tectonically more stable, Late Jurassic/Early Cretaceous Trøndelag Platform, the pre-Cenozoic succession is characterised by a condensed Cretaceous sequence, whilst in the Paleocene, thick wedges prograded from the Scandinavian mainland towards the deeper parts of the Møre and northern Nordland sea areas. Towards the Fennoscandian Shield, the Cenozoic succession is deeply eroded (Blystad et al. 1995, Brekke 2000). In the Oligocene to Early Pliocene, there was a pronounced progradation of coastal plains along the inner Norwegian Sea continental shelf (the sandy Molo Formation). Fartherwest, on the continental shelf, fine-grained clastic sedimentation, partly contouritic, prevailed (Laberg et al 2005b, Map 1, Profile P10, Profile P11, Profile P12 and Profile P13).

The North Sea Basin is an epicontinental basin

Confined by the Scandinavian and British landmasses, with a marine connection in the north to the Norwegian-Greenland Sea. In the Norwegian sector, the basin comprises several major Mesozoic highs and grabens of which the Central Graben in its south-central region and the Viking Graben in the north are dominant (Fig. 6 and Fig. 7). These structures were formed during several periods of extensional tectonics during the Permian and the Mesozoic. This extension ceased in the Cretaceous and the basin was subjected to post-rift subsidence and filled by sediments derived from surrounding topographical highs. In the Paleocene-Eocene, the surrounding landmasses were uplifted and the North Sea Basin deepened. Deltaic sequences prograded into the deep basin from the Shetland Platform and West Norway. Progradation continued in the Oligocene and Miocene, but was more confined to depocentres which varied through time (Eidvin & Rundberg 2001 and 2007, Gregersen & Johannessen 2007, Rundberg & Eidvin 2005).

The Norwegian-Danish Basin

Is confined by the Fennoscandian Shield in the north and the Fennoscandian Border Zone, also known as the Sorgenfrei-Tornquist Zone, in the northeast. In the south, the Ringkøbing-Fyn High separates the Norwegian-Danish Basin and the North German Basin. The deepest part of the basin is located in the west towards the Central Graben (Fig. 7, Ziegler 1990, Rasmussen et al. 2005). The basin was formed during Permian tectonism and thick sections of salt were deposited (Ziegler 1982, 1990 and Berthelsen 1992). Reactivation of different structural elements took place in Triassic to Early Cretaceous times (Vejbæk & Andersen 1987, Berthelsen 1992, Thybo 2001). The depositional environment was characterised by progradation and retrogradation of a coastal plain resulting in alternating sand-rich shore face deposits and mud-dominated marine sediments (Nielsen 2003). Parts of the basin were inverted during the Late Cretaceous (Liboriusen et al. 1987, Mogensen & Korstgård 1993) and also in the Early Miocene (Rasmussen 2009). Furthermore, fission-track data and reactivation of salt structures indicate an Eocene–Oligocene tectonic phase. The Late Cretaceous–Paleogene period was dominated by a deep-marine depositional environment dominated by pelagic and hemi-pelagic deposits (Surlyk & Lykke-Andersen 2007, Heilmann-Clausen 1985). The tectonic phase at the Eocene-Olgocene transition was accompanied by progradation of Early-Late Oligocene deltas off southern Norway (Schiøler et al. 2007). The Early Miocene inversion resulted in widespread delta progradation from central Sweden and southern Norway, and major parts of the Norwegian-Danish Basin became a land area in the Early Miocene (Rasmussen 2004, 2009). Increased subsidence in the Mid Miocene resulted in flooding of the area and sedimentation of clay-dominated marine sediments. This was succeeded by progradation of the shoreline during both the latest Late Miocene and the Late Pliocene when the shoreline prograded towards the Central Graben. A distinct tilting of the Norwegian-Danish Basin commenced in the late Neogene (Jensen & Schmidt 1992, Japsen 1993, Japsen et al. 2010). This was succeeded by a marked erosion of the marginal areas of the Norwegian-Danish Basin. Well 2/2-2 is situated in the deep part of the basin, and wells 9/12-1 and 11/10-1 are situated in marginal parts.

The Scandes mountains

Is a name commonly used for the present mountainous belt of western Scandinavia, which is underlain mainly by Proterozoic to Devonian metamorphic rocks. The paleogeography of this mountain range is debated, but regional mapping and well data show that western Scandinavia has been an important sediment source for the Norwegian shelf since the Paleocene. The Scandes mountains have two major culminations, one in central South Norway and one in northern Nordland, Troms and northern Sweden (Dehls et al., 2000). These culminations are referred to here as the southern and northern Scandes domes (Lidmar-Bergström 1999, Lidmar-Bergström & Näslund 2002).