Material and methods

T. Eidvin, F. Riis, E. S. Rasmussen & Y. Rundberg, 2013. New layout 2021

From the Norwegian continental shelf, Norwegian Sea, Svalbard, off Scoresby Sund (East-Greenland) and onshore Denmark, 1880 samples from 50 wells and boreholes and one outcrop have been investigated.

In most of the studied wells, the biostratigraphic analyses were performed largely on ditch-cutting samples. Sidewall cores were available in wells 16/1-4, 2/4-C-11, 6510/2-1 and 6610/3-1. Short conventional cores were available from wells 6305/4-1, 15/9-A-23, 2/4-C-11 and 2/2-2, boreholes 6704/12-GB1and 6403/5-GB1, and the gravity core 49-23. The ODP Site 987 drilling off Scoresby Sund was nearly continuously cored (Map 2). The ditch cuttings are usually sampled at 10 m intervals in the upper Cenozoic sections, and most of the available samples have been analysed. However, some of the samples stored at the NPD contain so little material that they could not be released for analyses. The Rødding and Hjøllund boreholes from onshore Denmark were sampled at one metre intervals for parts of sections, but with larger intervals in other parts.


Micropalaeontological investigations were based on analyses of planktonic and benthic foraminifera and Bolboforma. Pyritised diatoms were also used to establish the stratigraphy in Lower Miocene and Oligocene deposits. In some wells, palynological investigations were also performed.

The standard, Cenozoic, biostratigraphic zonation is based on planktonic foraminiferal and calcareous nannoplankton distributions established in tropical and sub-tropical areas. In middle and high latitudes, the assemblages become progressively less diverse and many key species are lacking (King 1983).

In this study, the fossil assemblages are correlated with the biozonation of King (1983, 1989), who outlined a micropalaeontological zonation for Cenozoic sediments in the North Sea. According to King (in prep.) some of the taxa names used in King (1983, 1989) have been revised. These are listed in Table 2. Gradstein & Bäckström’s (1996) faunal zonation from the North Sea and Haltenbanken is also used. In addition, a number of articles describing benthic foraminifera from onshore basins in the area surrounding central and southern North Sea are utilised. The zonations of planktonic foraminifera (Weaver 1987, Weaver & Clement 1986 and 1987, Spiegler & Jansen 1989) and Bolboforma (Spiegler & Müller 1992, Müller & Spiegler 1993, Spiegler 1999) from ODP and DSDP drillings in the Norwegian Sea and the North Atlantic are very important for the dating of the sediments. Correlation with these zones yields the most accurate age determinations, because the zones are calibrated with both nannoplankton and palaeomagnetic data.

Lithological analyses

The lithological analyses are based on visual examination of the samples prior to treatment, and of the washed, sieved and fractionated material after preparation.

Sr isotope analyses

Strontium isotope stratigraphy is used as an additional control for the biostratigraphic correlations. The 87Sr/86Sr ratio of seawater is very uniform on a global scale, which is a reflection of the long oceanic residence time of strontium (2-4 My), combined with a relatively short (≤ 2000 years) oceanic mixing time. This is an effective method particularly for the dating of Miocene and Oligocene sections. The method has best resolution in sediments older than 15 Ma. The reason for this is that the Sr isotopic composition of seawater changed rapidly with time during this period (e.g. Howard & McArthur 1997). For samples with ages younger than 8 Ma, the Sr isotope ages have to be treated with more caution. This is due to less variation in the Sr isotopic composition and a relatively flat curve between 2.5 and 4.5 Ma and also to some extent between 5.5 and 8 Ma (Hodell et al. 1991, Farrell et al. 1995).

In total, 825 samples were analysed for Sr isotopic composition. The analyses were carried out mainly on tests of calcareous foraminifera and fragments of molluscs (especially in sandy sections). In some samples, Bolboforma, fish teeth and Bryozoa fragments were also used. Ninety of these samples were taken from the Danish onshore boreholes and outcrops investigated palynologically by Dybkjær & Piasecki (2008, 2010, see Map 1 and Link to Danish Sr isotope ages). These analyses were based mainly on molluscs and mollusc fragments, but a few also on foraminiferal tests and shark teeth. The analytical work was conducted mainly at the Mass Spectrometry Laboratory, University of Bergen, Norway. The earliest analyses were performed at the Institute for Energy Technology (IFE) at Kjeller, Norway. All Sr isotopic ratios were normalised to 86Sr/88Sr = 0.1194 and to National Institute for Standard and Technology (NIST) 987 = 0.710248. Strontium values were converted to age estimates using the Strontium Isotope Stratigraphy (SIS) Look-up table of Howard & McArthur (1997); see McArthur et al. (2001) and Eidvin & Rundberg (2001, 2007) for more details about the method.

Seismic analyses

Seismic studies are based on a large number of regional 2-D lines and 3-D cubes from an extensive database covering most of the Norwegian continental margin and the Danish continental shelf. In addition, more than 1000 km of high-resolution, land-seismic data have been acquired across Jutland (Denmark) for the study of the Miocene deltas. Sequence boundaries identified on seismic data are tied to wells and boreholes by well velocity surveys carried out on the respective offshore wells (see profiles P1 to P13 in Map 1 and Map 2). Onshore boreholes in Denmark have been tied with seismic sections using a standard velocity of c. 1900 m/s. In the offshore areas, velocities are in the range of 1900 to 2100 m/s, except for the low-velocity deep-marine ooze. The principles of seismic stratigraphy of Brown & Fisher (1977) and concepts of sequence stratigraphy of Posamentier et al. (1988) and Hunt & Tucker (1992, 1995) have been applied.