?Upper Oligocene and Upper Pliocene in well 29/3-1
In well 29/3-1 (60º57’50.537’’N, 01º56’13.246’’E, Map 1) we recorded approximately 80 m with sediments of probably Late Oligocene age and approximately 150 m with Upper Pliocene deposits. The base of the ?Upper Oligocene and the top of the Upper Pliocene were not investigated. The units were investigated with 17 ditch-cutting samples at 10-20 meters intervals (Fig. 1).
Well summary figure for well 29/3-1
Biostratigraphy
?Upper Oligocene (870-approximately 790 m (log), Hordaland Group)
This unit is barren of in situ foraminifera and mulluscs. Abundant sponge spicules (rod-shaped and Geodia sp.) and a few radiolaria are the only fossils recorded. This is very similar to the upper part of the Oligocene section in the nearby well 34/10-17 (Map 1), and these units are correlated with wire-line logs and seismic data.
Upper Pliocene (approximately 790 m (log)-640 m, Nordland Group)
Benthic foraminifera of the Cibicides grossus-Elphidiella hannai assemblage and planktonic foraminifera of Neogloboquadrina atlantica (sinistral) assemblage 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 assemblage also includes Nonion affine (common), Cassidulina teretis (common), Elphidium albiumbilicatum, Cassidulina reniforme, Cibicides lobatulus and Bulimina marginata. The planktonic assemblage also includes Globigerina bulloides, Globorotalia inflata, Turborotalia quinqueloba and Neogloboquadrina pachyderma (dextral). 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. 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 Pliocene deposits older than 2.4 Ma (Spiegler & Jansen 1989). G. bulloides is also common in the warmest interglacials during the Pleistocene (Kellogg 1977).
Lithology
?Upper Oligocene (870-approximately 790 m (log), Hordaland Group)
The samples in this unit consist mainly of a medium to fine, glauconite-rich sand. Silt and clay are also quite common. In the upper part of the unit, glauconite is the dominant mineral in the sand fraction. In the lower part quartz is also quite common (Fig. 1).
Upper Pliocene (approximately 790 m (log)-640 m, Nordland Group)
The samples in the Upper Pliocene unit contain a sand-rich diamicton. Silt, clay and pebbles (mainly of crystalline rocks) are also quite common. Quartz dominates the sand fraction, but glauconite is also present throughout. The pebbles are interpreted as ice-rafted. According to Fronval & Jansen (1996), on the Vøring Plateau (Norwegian Sea) there is a marked increase in the supply of ice-rafted material after about 2.75 Ma which reflects the expansion of the northern European glaciers. The maximum age for the Upper Pliocene unit is therefore considered to be 2.75 Ma, belonging mainly to the Gelasian Stage.
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.
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.
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.
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.