Lower Eocene to Lower Miocene in well 6510/2-1
Modified after Eidvin et al. (2007).
Based on analyses of benthic foraminifera, dinoflagellate cysts and Sr isotopes, we recorded ?Lower Eocene sediments in two sidewall cores at 593 and 591 m, uppermost Lower to Middle Eocene sediments in five sidewall cores from 587 to 519 m, upper Middle Eocene sediments in a sidewall core at 511 m, ?Lower Oligocene sediments in a sidewall core at 502 m and Lower Miocene deposits in the sidewall cores at 480, 455 and 441 m in well 6510/2-1 (65°47’15.60’’N, 10°25’51.33’’E, Map 1, Fig. 1). There is probably a hiatus between the samples at 502 and 511 m. The top of the Lower Miocene was not investigated; see Eidvin et al. (2007) for the section from 722 to 591 m. The sidewall core samples in well 6510/2-1 were first presented in Eidvin et al. (2007), and in that paper the Miocene fossils in the samples from 480 to 441 m were interpreted to be reworked and a post-Mid Miocene age was suggested based on regional seismic correlations. New seismic correlations suggest that the correct age is Early Miocene and that the fossils are not reworked (Eidvin & Riis 2013).
Well summary figure for well 6510/2-1
?Lower Eocene (593 and 591 m, Brygge Formation)
According to Eidvin et al. (2007), an Early Eocene age (equivalent to NP Zone 12) can probably be extended down to 593 m based on the presence of the dinocysts Cribroperidinium tenuitabulatum, Deflandrea phosphoritica, Wetzeliella ovalis, Areosphaeridium dictyoplokkus and Rottnestina borussica (Fig. 1). According to Powell (1992) both A. dictyoplokkus and W. ovalis have their oldest appearances in beds equivalent to the middle Ypresian NP12 Zone. The presence of Alisocysta margarita and Isabelidinium ?viborgense at 593 m is taken as evidence of reworking from the Upper Paleocene. Reworking from the Lower Cretaceous is seen from the presence of Speetonia sp., Sirmiodinium grossii and Dingodinium cerviculum.
Uppermost Lower to Middle Eocene (587, 582, 575, 567 and 519 m, Brygge Formation)
According to Eidvin et al. (2007), the presence of the dinocyst Eatonicysta ursulae at 519 m gives an age not younger than early Mid Eocene (i.e. equivalent to NP15 Zone) at this level (Powell 1992). The presence of Hystrichosphaeropsis costae in the same sample support this interpretation (following the top range of this species given in Bujak, 1994). The youngest occurrence of Cerebrocysta magna further suggests an age not younger than middle NP15 Zone at 567 m. The presence of Adnatosphaeridium vittatum at 582 m indicates an age not older than middle NP12 Zone at this level. The occurrence of Dracodinium varielongitidum at 575 m, 582 m and 587 m suggests an age not older than middle Early Eocene (NP 12 Zone) down to 587 m. Deflandrea granulata is present between 575-587 m. The lowest occurrence of this species defines the base of the Deflandrea sp. B Zone of Manum et al. (1989). The underlying A. vittatum Zone of Manum et al. (1989) was defined as the interval from the lowest occurrence of A. vittatum to the lowest occurrence of Deflandrea sp. B (herein recorded as D. granulata). In well 6510/2-1 A. vittatum has only been found in a single sample at 582 m, together with D. granulata. While Manum et al. (1989) dated the oldest occurrence of A. vittatum as Middle Eocene, Powell (1992) placed the FAD of this species within the mid Ypresian.
Upper Middle Eocene (511 m, Brygge Formation)
The dinocyst H. porosa found in this sample is a good marker for the Middle Eocene (i.e. upper NP16 to NP17 Zones, Powell 1992, Bujak 1994). The presence of Pthtanoperidinium clinthridum and common Pthtanoperidinium geminatum support this age interpretation. In their study of ODP Site 643 on the Vøring Plateau, Manum et al. (1989) found H. porosa in one single sample (104-643-51-1) within their Middle Eocene Areosphaeridium arcuatum Zone (Eidvin et al., 2007).
?Early Oligocene (502 m, Brygge Formation)
The presence of the dinocyst Areoligera semicirculata gives firm evidence of an age not younger than Early Oligocene (i.e. 28.5 Ma according to Williams & Manum 1999 and Eidvin et al. 2007).
Lower Miocene (480-441 m, Molo Formation)
According to Eidvin et al. (2007) the benthic foraminifera of the Astigerina guerichi staeschei assemblage and dinocysts of the Cyclopsiella granosa zone supported by a strontium-isotope age date this unit to Early Miocene. The two sidewall cores at 480 and 455 m contained unconsolidated sands saturated with drillings fluids. It was not possible to remove the drillings fluids during the microfossil preparation process. These fluids were probably the source of some Pleistocene and Holocene fossils. The uppermost sample is barren of foraminifera. Probably in situ A. guerichi staeschei is recorded at 480 (common) and 455 m. P. bulloides at 480 m is also probably in situ. Pleistocene and Holocene caved foraminifera include Bulimina marginata, Islandiella islandica, Uvigerina peregrina, Hyalina baltica and N. Pachyderma (sinistral, encrusted). The in situ benthic foraminiferal assemblage can probably be correlated with Zone NSB 10 King (1989) and probably with Zone NSR 8B of Gradstein & Bäckström (1996) from the North Sea area.
The two uppermost samples are characterised by abundant (441 m) to common (455 m) specimens of the dinocysts C. granosa, together with Paralacaniella indentata. All the samples also contain common reworked Paleogene and caved Plio-Pleistocene dinocysts. Matsuoka & Head (1992) reported an Early to Late Miocene age for C. granosa based on several published observations in the North Atlantic Ocean.
Sr isotope stratigraphy
Sr isotope analysis was performed on ten specimens of A. guerichi staeshei from the sidewall core at 480 m. The obtained 87Sr/86Sr ratios gave an age of 17.1 Ma (Early Miocene, Table 1, Fig. 1), which supports the biostratigraphical correlations.
|Litho. unit||Sample (DC)||Corrected 87/86Sr||Age (Ma)||Analysed fossil species|
|Molo Fm||480 m||0.708680||17.06||Ten tests of A. guerichi staeshei|
Table 1: Strontium isotope data from well 6510/2-1 according to Eidvin et al (2007). The sample was analysed at the University of Bergen. Sr ratio was corrected to NIST 987 = 0.710248. The numerical age was derived from the SIS Look-up Table Version 3:10/99 of Howard & McArthur (1997). NIST = National Institute for Standard and Technology.
The sidewall cores at 593, 591, 587, 582, 575, 567, 519 and 502 m which represent the Brygge Formation of ?Early Eocene to ?Early Oligocene age contain mostly muddy, micaceous siltstones. The sample at 511 m of the Brygge Formation, however, is quite sandy, but the sand is not as coarse as the sand of the Molo Formation. The sand contains quartz, mica and a smaller portion of glauconite.
The sidewall cores at 480, 455 and 441 m, which represent the Molo Formation, contain quite coarse sand. The sand contains mainly glauconite (dominant) and quartz grains, which are angular to subangular. Many of the quartz grains are rust-stained.
Bujak, J.P., 1994: New dinocyst taxa from the Eocene of the North Sea. Journal of micropalaeontology, 13, 119-131.
Eidvin, T. & Riis, 2013: The Lower Oligocene – Lower Pliocene Molo Formation on the inner Norwegian Sea continental shelf (Extent and thickness, age from fossil and Sr isotope correlations, lithology, paleobathymetry and regional correlation). NGF Abstracts and proceedings, no. 1, 2013, p. 31. Poster available from the internet: http://www.npd.no/Global/Norsk/3-Publikasjoner/Presentasjoner/NGF-Vinterkonferanse-2013/Poster-4-til-NGF-vintermotet-nett.pdf
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
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.
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.
Matsuoka, K. & Head, M. J., 1992: Taxonomic revision of the Noegene marine palynomorphs Cyclopsiella granosa (Matsuoka) and Batiacasphaera minuta (Matsuoka), and a new species of Pyxidiniopsis Habib (Dinophyceae) from the Miocene of the Labrador Sea.In M. J. Head & J. H. Wrenn, Neogene and Quaternary Dinoflagellate Cysts and Acritrachs (pp.165-180). American Association of Stratigraphic Palynologists Foundation, Dallas.
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.
Williams, G. L. & Manum, S. B., 1999: Late Oligocene to Early Miocene dinocyst stratigraphy of ODP Site 985 (Norwegian Sea). Proceedings of the Ocean Drilling Program, Scientific Results, 16, 99-109.