Lower Oligocene to Upper Pliocene in well 6407/9-2

Modified after Eidvin et al. (2007).

Based on analyses of benthic and planktonic foraminifera, pyritised diatoms and dinoflagellate cysts in well 6407/9-2 (64º24’01.31’’N, 07º48’11.26’’E, Map 1), we recorded a 40 m-thick unit of Lower Oligocene sediments, a 55 m-thick unit of Lower Pliocene deposits and 45 m with Upper Pliocene sediments. There is an unconformity between the Lower and Upper Pliocene. The base of the Lower Oligocene and the top of the Upper Pliocene were not investigated. The units were investigated with 15 ditch-cutting samples at ten metre intervals (Fig. 1).

Well summary figure for well 6407/9-2

Biostratigraphy

Lower Oligocene (900-860 m, Brygge Formation)

According to Eidvin et al. (2007), dinoflagellate cysts attributed to the Svalbardella cooksoniae Zone and the Areoligera semicirculata Zone and pyritised diatoms of the Diatom sp. 3 assemblage give an Early Oligocene age to this unit (Fig. 1). The benthic foraminiferal fauna includes Alabamina scitula and Spirosigmoilinella compressa (agglutinated). The unit is correlated with the lower part of Subzone NSP 9c and probably Zone NSA 7 or 8 of King (1989) from the North Sea and probably Zone NSR 7A or 7B of Gradstein & Bäckström (1996) from the North Sea and Haltenbanken area. Manum et al. (1989) found that S. cooksonia was restricted to their Early Oligocene Chiropteridium lobospinosum Zone in ODP Hole 643 in the Norwegian Sea. According to Powell (1992), the LAD of A. semicirculata lies within the lower NP25 calcareous nannoplankton biozone in Britain and in the North Sea area. Manum et al. (1989) found that the LAD of this species (named Glaphyrocysta intricata in their publication) corresponded to the upper boundary of their Early/Late Oligocene Areosphaeridium? actinocoronatum in ODP Hole 643 in the Norwegian Sea. The LAD of this species also defines the upper boundary of the Oli4 Zone of Poulsen et al. (1996) as defined in ODP Hole 908 on the Hovgaard Ridge between Svalbard and NE Greenland.

Lower Pliocene (860-805 m (log), Molo Formation)

According to Eidvin et al. (2007), benthic calcareous foraminifera of the Monspeliensina pseudotepida assemblage and Eponides pygmeus assemblage indicate an Early Pliocene age for this unit (Fig. 1). The planktonic foraminiferal fauna includes N. atlantica (sinistral) and G. bulloides. The benthic foraminiferal assemblages are correlated with Subzone NSB 14a of King (1989) and Zone NSR 12A of Gradstein & Bäckström (1996) from the North Sea.

Upper Pliocene (805 (log)-760 m, Naust Formation)

According to Eidvin et al. (2007), benthic foraminifera of the Elphidiella hannai assemblage and planktonic foraminifera of the Neogloboquadrina atlantica (sinistral) assemblage (upper main part) give a Late Pliocene age (on the time scale of Berggren et al. 1995) for this unit (Fig. 1). In addition to the nominate species, the benthic foraminiferal assemblage also includes Cibicides grossus, Elphidium excavatum, Cassidulina reniforme, Cibicides lobatulus, Nonion affine, Bulimina marginata and Elphidium albiumbilicatum. The benthic foraminiferal fauna is correlated with Subzone NSB 15a of King (1989, North Sea) and Zone NSR 12 of Gradstein & Bäckström (1996, North Sea and Haltenbanken area). Spiegler & Jansen (1989) described a N. atlantica (sinistral) Zone from the Vøring Plateau (Norwegian Sea) from Upper Miocene to Upper Pliocene deposits. The LAD of N. atlantica (sinistral) in that area is approximately 2.4 Ma.

Lithology

Lower Oligocene (900-860 m, Brygge Formation)

Clay dominates the samples in this unit. Small portions of sand (mainly glauconitic) and silt are also recorded (Fig. 1). Some of the sand and silt may be caved from the Lower Pliocene unit.

Lower Pliocene (860-805 m (log), Molo Formation)

Clay is present, but is less common than in the Lower Oligocene. The upper part contains a considerable proportion of sand (mainly quartzose) and pebbles of crystalline rocks, but most of the sand and all the pebbles are probably caved from the glacial deposits in the Upper Pliocene unit. In the lower part glauconitic sand is common (Fig. 1).

Upper Pliocene (805 (log)-760 m, Naust Formation)

The Upper Pliocene unit contains a clay-rich diamicton which is also rich in sand, silt and pebbles. Most of the pebbles are of crystalline rocks, but some are also of sedimentary rocks. These pebbles are interpreted as ice-rafted and indicate that the sediments were deposited after the marked increase in the supply of ice-rafted detritus to the Norwegian Sea, which started at about 2.75 Ma (Fronval & Jansen 1996).

References

Berggren, W. A., Kent, D. V, Swisher, C. C., III & Aubry, M.- P., 1995: A Revised Cenozoic Geochronology and Chronostratigraphy. In Berggren, W. A. et al. (eds.): Geochronology Time Scale and Global Stratigraphic Correlation. Society for Sedimentary Geology Special Pulication 54, 129-212.

Eidvin, T., Bugge, T. & Smelror, M., 2007: The Molo Formation, deposited by coastal progradation on the inner Mid-Norwegian continental shelf, coeval with the Kai Formation to the west and the Utsira Formation in the North Sea. Norwegian Journal of Geology 87, 75-142. Available from the internet: : http://www.npd.no/Global/Norsk/3-Publikasjoner/Forskningsartikler/Eidvin_et_al_2007.pdf

Fronval, T. & Jansen, E., 1996: Late Neogene paleoclimates and paleoceanography in the Iceland-Norwegian Sea: evidence from the Iceland and Vøring Plateaus. In Thiede, J., Myhre, A. M., Firth, J. V., John, G. L. & Ruddiman, W. F. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results 151: College Station, TX (Ocean Drilling Program), 455-468.

Gradstein, F. & Bäckström, S., 1996: Cainozoic Biostratigraphy and Paleobathymetry, northern North Sea and Haltenbanken. Norsk Geologisk Tidsskrift 76, 3-32.

King, C., 1989: Cenozoic of the North Sea. In Jenkins, D. G. and Murray, J. W. (eds.), Stratigraphical Atlas of Fossils Foraminifera, 418-489. Ellis Horwood Ltd., Chichester.

Manum, S. B., Boulter, M. C., Gunnarsdottir, H., Ragnes, K. & Scholze, A., 1989: Eocene

to Miocene palynology of the Norwegian Sea (ODP Leg 104). Proceedings of the

Ocean Drilling Program, Scientific Results, 104, 611-622.

Poulsen, N. E., Manum, S. B., Williams, G. L. & Ellegaard, M., 1996: Tertiary dinoflagellate biostratigraphy of Sites 907, 908, and 909 in the Norwegian. Greenland Sea. Proceedings of the Ocean Drilling Program, Scientific Results, 151, 255-287.

Powell, A. J., 1992: Dinoflagellate cysts of the Tertiary System. In Powell, A.J. (ed.) A

Stratigraphic Index of Dinoflagellate Cysts. Chapmann and Hall, London, 155-251.

Spiegler, D. & Jansen, E., 1989: Planktonic Foraminifer Biostratigraphy of Norwegian Sea Sediments: ODP Leg 104. In Eldholm, O., Thiede, J., Tayler, E., et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results 104: College Station, TX (Ocean Drilling Program), 681-696.