Upper Oligocene to Upper Pliocene in well 15/12-3
Modified after Eidvin & Rundberg (2007).
Based on analyses of benthic and planktonic foraminifera, Bolboforma, pyritised diatoms and Sr isotopes in well 15/12-3 (58º14'36.59''N, 01º52'45.67''E, Map 1), we recorded 60 m with Upper Oligocene sediment, 160 m with Lower Miocene deposits, 190 m with Middle Miocene deposits, 100 m with Upper Miocene deposits, 90 m with Lower Pliocene sediments and 220 m with Upper Pliocene deposits. The base of the Upper Oligocene and the top of the Upper Pliocene were not investigated. The units are investigated with 58 ditch-cutting samples at mainly ten metre intervals. However, in some parts, where the stored samples are depleted to the archive limit, there are 20 metre intervals (Figs. 1 and 2). See Eidvin & Rundberg (2007) for the section from 680 to 200 m. In that paper there is also a more detailed stratigraphy of all the units (including fossil range charts).
Well summary figure for well 15/12-3, fig 1
Well summary figure for well 15/12-3, fig 2
Biostratigraphy
Upper Oligocene (1520-1460 m, Hordaland Group)
Pyritised diatoms attributed to the Diatom sp. 3 assemblage and benthic foraminifera of the Annectina biedai - Turrilina alsatica assemblage, together with one Sr isotope age (26.8 Ma) from 1520-1500 m date this unit to Late Oligocene (Fig. 1). In addition to the nominate species, the benthic foraminiferal fauna include B. eocenicus, C. placenta, R. arnei, Valvulineria petrolei and R. orbiculare. The planktonic foraminiferal fauna include G. praebulloides, G. ciperoensis, G. angustiumbilicata and G. woodi. The diatom assemblage is correlated with the upper part of Subzone NSP 9c, and the benthic foraminiferal assemblage is correlated with Zone NSB 8 and NSA 9 of King (1989) and probably Zone NSR 8A and the upper part of Zone 7B of Gradstein & Bäckström (1996) from the North Sea.
Lower Miocene (1460-1300 m, Hordaland Group and the lowermost part of Nordland Group)
Benthic foraminifera of the Plectofrondicularia seminuda assemblage and Uvigerina tenuipustulata assemblage, pyritised diatoms of the Diatom sp. 4 assemblage and planktonic foraminifera of the Globorotalia zealandica - Globigerina ciperoensis assemblage, together with two Sr ages, give an Early Miocene age to this unit (Fig. 1). In addition to the nominate species the Plectofrondicularia seminuda assemblage includes Bolivina cf. antiqua. The Globorotalia zealandica - Globigerina ciperoensis assemblage includes G. praescitula. The Plectofrondicularia seminuda assemblage is correlated with Zone NSB 9, the Uvigerina tenuipustulata assemblage is correlated with Zone NSB 10, the Diatom sp. 4 assemblage is correlated with Zone NSP 10 and the Globorotalia zealandica - Globigerina ciperoensis assemblage is correlated with Zone NSP 11 of King (1989) from the North Sea. These assemblages are also correlated with Zone NSR 8B and the lower part of Zone NSR 9A of Gradstein & Bäckström (1996) from the same area.
Middle Miocene (1300-1110 m, Nordland Group and the lowermost part of Utsira Formation)
Benthic foraminifera of the Astigerina guerichi staeshei assemblage and Uvigerina pygmea langenfeldensis assemblage, planktonic foraminifera of the Globigerina praebulloides assemblage and Bolboforma of the Bolboforma badenensis - B. reticulata assemblage, together with a number of Sr isotope ages give a Mid Miocene age to this unit (Fig. 1). In addition to the nominate species the benthic foraminiferal assemblages also include B. elongata. The Astigerina guerichi staeshei assemblage is correlated with Zone NSB 11 of King (1989, North Sea), probably Zone FD of Doppert (1980, the Netherlands) and probably Zone NSR 9A of Gradstein & Bäckström (1996, North Sea). Uvigerina pygmea langenfeldensis assemblage is correlated with Subzone 13a and probably Zone 12 of King (1989, North Sea). G. praebulloides is known from Oligocene to lower Upper Miocene (common in Middle Miocene) deposits in the North Atlantic (Poore 1979) and from Oligocene to lower Middle Miocene deposits in the North Sea (Gradstein & Bäckström, 1996). Spiegler & Müller (1992) described a B. badenensis Zone and a B. reticulata Zone from the North Atlantic and Müller & Spiegler (1993) described a B. badenensis/B. reticulata Zone from the Vøring Plateau in deposits with an age of slightly more than 14 to 11.7 Ma.
Upper Miocene (1110-1010 m, Utsira Formation)
Benthic foraminifera of the Uvigerina venusta saxonica (lower part) and planktonic foraminifera of the Neogloboquadrina atlantica (dextral) - Neogloboquadrina acostaensis assemblage together with several Sr isotope ages, give a Late Miocene age to this unit (Fig. 1). The benthic foraminiferal fauna also include G. subglobosa and F. boueanus. Spiegler & Jansen (1989) described a lower N. atlantica (dextral) Zone from Upper Miocene sediments on the Vøring Plateau, and Weaver & Clement (1987) reported a N. atlantica (dextral)/N. acostaensis Zone from Upper Miocene sediments in the North Atlantic. The benthic foraminiferal fauna is correlated with lower part of Subzone NSB 13b (King 1989, North Sea).
Lower Pliocene (1010-900 m, Utsira Formation and Nordland Group)
Benthic foraminifera of the Uvigerina venusta saxonica (upper part) and planktonic foraminifera of the Globorotalia puncticulata assemblage and Neogloboquadrina atlantica (sinistral) assemblage (lower part), together with a few Sr isotope ages, give an Early Pliocene age for this unit (Fig. 1). The benthic foraminiferal fauna also include M. pseudotepida, G. subglobosa and F. boueanus. The benthic foraminiferal fauna is correlated with the upper part of Subzone NSB 13b of King (1989, North Sea). Weaver & Clement (1986) described a Globorotalia puncticulata assemblage in deposits with an age of 4.6-2.5 Ma from the North Atlantic.
Upper Pliocene (900-680 m, Nordland Group)
Benthic foraminifera of the Cibicides grossus assemblage and planktonic foraminifera of the Neogloboquadrina atlantica (sinistral) assemblage (upper part), Globigerina bulloides assemblage, upper Neogloboquadrina atlantica (dextral) assemblage and Neogloboquadrina pachyderma (dextral) assemblage give a Late Pliocene age (on the time scale of Berggren et al. 1995) for this unit (Fig. 2). 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 of the last 0.5 Ma in the North Atlantic (Kellogg 1977). An upper N. atlantica (dextral) Zone is described from the Vøring Plateau in Upper Pliocene deposits, and is dated to 2.4-1.9 Ma (Spiegler & Jansen 1989). A latest Pliocene N. pachyderma (dextral) Zone is described by King (1989) for the North Sea, by Weaver (1987) and Weaver & Clement (1986) from the North Atlantic and by Spiegler & Jansen (1989) from the Vøring Plateau. On the Vøring Plateau the zone is dated to 1.9-1.8 Ma.
Sr isotope stratigraphy
Nine samples based on mollusc fragments from six depths, and twelve samples based on foraminifera and Bolboforma from nine depths were analysed in well 15/12-3. The obtained 87Sr/86Sr ratio from 1520-1500 m (based on benthic foraminifera) gave an age of 26.8 Ma (Late Oligocene) which supports the biostratigraphical correlations (Table 1, Fig. 1). Two samples from 1310 m (one based one benthic foraminifera and one based on planktonic foraminifera) both gave 17.0 Ma (Early Miocene) which also fits very well with the biostratigraphical correlations (Table 1, Fig. 1). Seven samples, based on benthic foraminifera, were taken from the unit which were given a Mid Miocene age by the biostratigraphical correlations. The data showed fairly consistently an increasing age with depth from 10.6 Ma in the topmost part to 14.8 Ma near the base of the section (Table 1, Fig. 1), and these ages are also in agreement with the age given by the biostratigraphical correlations.
Fourteen samples (eleven based on mollusc fragments and three based on Bolboforma) were analysed from the sandy Utsira Formation. The data showed no clear trend of successively older age with depth. In the upper part (980-940 m), however, two samples gave ages of 4.9 and 3.5 Ma, supporting the Early Pliocene age indicated by the biostratigraphical correlations, whereas two other samples gave older ages of 10.6 and 9.9 Ma. In the middle part (1060-1020 m), three samples gave ages of 17.2, 16.7 and 14.6 Ma, suggesting reworking, similarly to samples from the Utsira sand in well 16/1-2. In the lower part of the sand (1120-1100 m), six samples gave fairly consistent ages between 11.8 and 8.9 Ma. Correlation based on the last occurrence of B. badenensis indicates a latest Mid Miocene age of about 11.7 Ma for this part of the Utsira sand (1130-1110 m, Table 1, Fig. 1).
Well 15/12-3
| Litho. Unit | Sample (DC) | Corrected 87/86Sr | 2S error | Age (Ma) | Comments | Analysed fossils |
| Utsira Fm | 940 m | 0.709061 | 0.000009 | 3.52 | Four mollusc fragments | |
| Utsira Fm | 940 m | 0.708873 | 0.000009 | 10.59 | Reworked | Four mollusc fragments |
| Utsira Fm | 980 m | 0.708891 | 0.000008 | 9.42 | Four mollusc fragments | |
| Utsira Fm | 980 m | 0.709041 | 0.000008 | 4.86 | Five mollusc fragments | |
| Utsira Fm | 1020 m | 0.708706 | 0.000009 | 16.70 | Reworked | Four mollusc fragments |
| Utsira Fm | 1020 m | 0.708791 | 0.000009 | 14.61 | Reworked | Five mollusc fragments |
| Utsira Fm | 1060 m | 0.708897 | 0.000009 | 9.67 | Four mollusc fragments | |
| Utsira Fm | 1060 m | 0.708670 | 0.000009 | 17.17 | Reworked | Four mollusc fragments |
| Utsira Fm | 1100 m | 0.708839 | 0.000009 | 11.80 | Four mollusc fragments | |
| Utsira Fm | 1100 m | 0.708916 | 0.000009 | 8.87 | Five mollusc fragments | |
| Utsira Fm | 1110 m | 0.708874 | 0.000014 | 10.55 | Approximately 50 tests of B. badenensis and B. clodiusi | |
| Utsira Fm | 1120 m | 10a | Approximately 26 tests of B. clodiusi | |||
| Utsira Fm | 1120 m | 0.708882 | 0.000013 | 10.26 | Approximately 45 tests of B. badenensis and B. clodiusi | |
| Utsira Fm | 1120 m | 0.708870 | 0.000008 | 10.69 | Four mollusc fragments | |
| Nordland Gr | 1160 m | 10.6a | Approximately 26 tests of B. subfragori and B. fragori | |||
| Nordland Gr | 1180 m | 0.708869 | 0.000014 | 10.73 | Approximately 45 tests of B. badenensis and B. clodiusi | |
| Nordland Gr | 1180 m | 0.708913 | 0.000021 | 9.00 | Approximately 30 tests of U. pygmea langenfeldensis | |
| Nordland Gr | 1200 m | 0.708905 | 0.000022 | 9.34 | 24 tests of U. pygmea langenfeldensis | |
| Nordland Gr | 1200 m | 0.708852 | 0.000012 | 11.27 | Approximately 60 tests of B. badenensis and B. clodiusi | |
| Nordland Gr | 1220 m | Approximately 50 tests of B. badenensis | ||||
| Nordland Gr | 1250-1280 m | 14.8a | Six tests of A. guerichi staeshei | |||
| Hordal. Gr | 1310 m | 17.0a | 18 tests of U. tenuipustulata | |||
| Hordal. Gr | 1310 m | 17.0a | 20 tests of G. woodi | |||
| Hordal. Gr | 1500, 1520 m | 26.8a | Eight tests of G. soldanii girardana |
Table 1: Strontium isotope data from well 15/12-3. 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. Modified from Eidvin & Rundberg (2007), a from Nødtvedt (1999).
Lithology
Upper Oligocene to the uppermost part of Middle Miocene (1520 to approximately 1130 m, Hordaland and Nordland Group)
Clay dominates this part. Minor sand and silt are also recorded throughout. Limestone is recorded in some samples in the lower and middle parts of the unit (Fig. 1).
Uppermost part of Middle Miocene to Lower Pliocene (approximately 1130 to 900 m, Utsira Formation and Nordland Group)
Light grey sand dominates the Utsira Formation. The sand contains mainly quartz grains, but some glauconite and mica grains are also present. The lower part of the unit also contains quite a large proportion of silt and clay. Mollusc fragments are common in the middle and upper parts. The uppermost Lower Pliocene sample (900 m) is just above the Utsira Formation and contains more fine-grained material (Fig. 1).
Upper Pliocene (900 to 680 m, Nordland Group)
The samples in the Upper Pliocene section contain a clay-rich diamicton with some sand and silt and minor pebbles.
References
Doppert, J. W. C., 1980: Lithostratigraphy and biostratigraphy of marine Neogene deposits in the Netherlands. Mededelingen Rijks Geologische Dienst 32-16, 2, 3-79.
Eidvin, T. & Rundberg, Y., 2007: Post-Eocene strata of the southern Viking Graben, northern North Sea; intergrated biostratigraphic, strontium isotopic and lithostratigraphic study. Norwegian Journal of Geology 87, 391-450. Available from the internet: http://www.npd.no/Global/Norsk/3-Publikasjoner/Forskningsartikler/Eidvin_and_Rundberg_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.
Jansen, E. & Sjøholm, J., 1991: Reconstruction of glaciation over the past 6 Myr from ice- borne deposits in the Norwegian Sea. Nature 349, 600-603.
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.
Müller, C. & Spiegler, D., 1993: Revision of the late/middle Miocene boundary on the Voering Plateau (ODP Leg 104). Newsletter on Stratigraphy, 28 (2/3), 171-178.
Nødtvedt, A. B., 1999: Termisk utvikling gjennom kenozoikum langs den norske kontinentalmarginen. Cand. scient. thesis, University of Bergen, 106 pp.
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.
Spiegler, D. & Müller, C., 1992: Correlation of Bolboforma zonation and nannoplankton stratigraphy in the Neogene of the North Atlantic: DSDP sites 12-116, 49-408, 81-555 and 94-608. Marine Micropaleontology 20, 45-58.
Weaver, P. P. E., 1987: Late Miocene to Recent planktonic foraminifers from the North Atlantic: Deep Sea Drilling Project Leg 94. Initial Reports of the Deep Sea Drilling Project 94, 703-727.
Weaver, P. P. E. & Clement, B. M., 1986: Synchronicity of Pliocene planktonic foraminiferid datums in the North Atlantic. Marine Micropalaeontology 10, 295-307.
Weaver, P. P. E. & Clement, B. M., 1987: Magnetobiostratigraphy of planktonic foraminiferal datums: Deep Sea Drilling Project Leg 94, North Atlantic. In Ruddiman, W. F., Kidd, R. B., Thomas, E., et al. (eds.): Initial Reports of the Deep Sea Drilling Project 94, 815-829.