Lower Oligocene to Upper Pliocene in well 6407/9-1
Modified after Eidvin et al. (2007).
Based on analyses of benthic and planktonic foraminifera, dinoflagellate cysts and Sr isotopes in well 6407/9-1 (64º24’01.31’’N, 07º48’11.26’’E, Map 1), we recorded 165 m with Lower Oligocene deposits, a 35 m-thick unit with Upper Miocene – Lower Pliocene sediments, 30 m with Lower Pliocene sediments and 50 m with Upper Pliocene deposits. The base of the Lower Oligocene and the top of the Upper Pliocene were not investigated. The units were investigated with 24 ditch-cutting samples which were sampled at ten metre intervals, but some samples are missing and there are no samples between 790 and 820 m in the middle of the Molo Formation (Fig. 1).
Well summary figure for well 6407/9-1
Biostratigraphy
Lower Oligocene (990-825 m (log), Brygge Formation)
According to Eidvin et al. (2007), benthic calcareous foraminifera of the Rotaliatina bulimoides assemblage, Gyroidina soldanii mamillata assemblage, Turrilina alsatica assemblage and Gyroidina soldanii girardana assemblage, and dinoflagellate cysts of the Areoligera semicirculata Zone supported by a strontium-isotope age obtained from 900 m date this unit to Early Oligocene (Fig. 1). The benthic foraminiferal assemblages are correlated with Zone NSB 7 of King (1989) from the North Sea and Zone NSR 7A or 7B of Gradstein & Bäckström (1996) from the North Sea and Haltenbanken area. 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.
Upper Miocene-Lower Pliocene (825 (log)-790 m, Molo Formation)
According to Eidvin et al. (2007), dinoflagellate cysts attributed to the Achomosphaera sp. 1 Assemblage Zone (upper, main part), supported by a strontium-isotope age obtained from 790 m, give a Late Miocene to Early Pliocene age to this unit (Fig. 1). Achomosphaera sp. 1 has previously been consistently recorded in Upper Miocene-Lower Pliocene strata at ODP Sites 907, 908 and 909 in the Norwegian-Greenland Sea (Poulsen et al. 1996). The occurrence of Achomosphaera sp. 1 in Lower Oligocene deposits is probably caved (Fig. 1).
Lower Pliocene (790-760 m, Molo Formation)
According to Eidvin et al. (2007), benthic calcareous foraminifera of the Eponides pygmeus-Sphaeroidina bulloides assemblage and dinoflagellate cysts of the Reticulatosphaera actinocoronata Zone indicate an Early Pliocene age for this interval (Fig. 1). The planktonic foraminiferal fauna includes G. bulloides and N. atlantica (sinistral). The benthic foraminiferal assemblage is tentatively correlated with the lower part of Subzone 14a of King (1989) from the North Sea. The presence of the dinocyst R. actinocoronata, together with the thermophilic species Operculodinium israelianum, suggests an Early Pliocene age for this sample.
Upper Pliocene (760-710 m, Naust Formation)
According to Eidvin et al. (2007), benthic foraminifera of the Elphidiella hannai assemblage and planktonic foraminifera of the Globigerina bulloides assemblage (upper 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, 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). A G. bulloides Zone is described from the North Atlantic (DSDP Leg 94) in Pliocene sediments as young as 2.2 Ma (Weaver & Clement 1986). On the Vøring Plateau G. bulloides is common in Late Miocene to Pliocene deposits older than 2.4 Ma (Spiegler & Jansen 1989). G. bulloides is also common in the warmest interglacials of the Pleistocene in the North Atlantic (Kellogg 1977).
Sr isotope stratigraphy
Calcareous benthic foraminifera from 900 and 790 m were analysed for Sr isotopes. The obtained 87Sr/86Sr ratios from the sample at 900 m gave an age of 32.4 Ma (Early Oligocene) and the sample at 790 m gave an age of 6.0 Ma (latest Late Miocene, Table 1, Fig. 1), which both support the biostratigraphical correlation.
Well 6407/9-1
| Litho. Unit | Sample (DC) |
Corrected 87/86Sr |
2S error | Age (Ma) | Analysed fossil species |
| Molo Fm | 790 m | 0.708989 | 0.000023 | 6.0 | 16 tests of Spaeroidina bulloides, Eponides pygmeus, Ceratobulimina contraria and G. subglobosa |
| Hordaland Gr | 900 m | 0.707972 | 0.000014 | 32.4 | 25 tests of Bolivina cf. antique, T. alsatica, Alabamina scitula and G. soldanii girardana |
Table 1: Strontium isotope data from well 6407/9-1. The samples were analysed at the University of Bergen. Sr ratios were corrected to NIST 987 = 0.710248. The numerical ages were derived from the SIS Look-up Table Version 3:10/99 of Howard & McArthur (1997). NIST = National Institute for Standard and Technology.
Lithology
Lower Oligocene (990-825 m (log), Brygge Formation)
The ditch-cutting samples in this unit are dominated by clay. Small portions of sand (mainly glauconitic) and silt are also recorded throughout (Fig. 1). The two uppermost samples (840 and 830 m) are rich in glauconitic sand, but most of this is probably caved from Upper Miocene to Lower Pliocene deposits.
Upper Miocene to Lower Pliocene (825 (log)-760 m, Molo Formation)
Clay is present, but is less common in this unit than in the Lower Oligocene. The upper part contains a considerable proportion of sand (mainly quartzose) and pebbles of crystalline rocks (probably caved). The lower part is rich in glauconitic sand (Fig. 1).
Upper Pliocene (760-710 m, Naust Formation)
The Upper Pliocene unit contains a clay-rich diamicton which is also rich in sand, silt and pebbles. The pebbles are mostly of crystalline rocks, but some of sedimentary rocks are also recorded. 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: https://www.npd.no/globalassets/1-npd/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.
Howarth, R. J. & McArthur, J. M., 1997: Statistics for Strontium Isotope Stratigraphy: A Robust LOWESS Fit to Marine Sr-Isotope Curve for 0 to 206 Ma, with Look-up table for Derivation of Numeric Age. Journal of Geology 105, 441-456.
Kellogg, T. B., 1977: Paleoclimatology and Paleo-oceanography of the Norwegian and Greanland Seas: The Last 450,000 years. Marine Micropalaeontology 2, 235-249.
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.
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.
Weaver, P. P. E. & Clement, B. M., 1986: Synchronicity of Pliocene planktonic foraminiferid datums in the North Atlantic. Marine Micropalaeontology 10, 295-307.