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

In this NPD Bulletin, the stratigraphy of Oligocene to Lower Pliocene deposits from Svalbard and East Greenland in the north to Denmark in the south is presented.

To define the upper limit of the successions, we have also included the investigations of the Upper Pliocene in most wells. This publication includes a synthesis of data from 47 wells and boreholes from the entire Norwegian shelf, one outcrop from northwestern Svalbard, one ODP borehole off East Greenland and two stratigraphic boreholes from onshore Denmark (Map 1, Map 2, Fig. 1, Fig. 2, Fig. 3, Fig. 4 and Fig. 5). The descriptions are based on a number of papers and other publications which include biostratigraphic (mainly based on foraminifera and Bolboforma), lithostratigraphic and seismostratigraphic studies and Sr isotope analyses, including Eidvin (2009), Eidvin & Rundberg (2001 and 2007), Eidvin et al. (1993, 1998 a, b and c, 1999, 2000, 2007, 2010) and Rundberg & Eidvin (2005). Later, some wells were partly re-analysed or re-interpreted, and new data from a number of wells and stratigraphical boreholes are now included. Most biostratigraphic analyses of wells, boreholes and outcrops have been integrated with wire-line log and seismic data. The deposits of the Norwegian continental shelf and onshore Denmark are correlated to the deep-sea record.

A detailed understanding of the Oligocene to Pliocene stratigraphy is important in reconstructing the geological history of the North Sea Basin and the uplift and erosion of the Fennoscandian Shield. It can also be applied to petroleum exploration and CO2 sequestration. For these purposes, in most areas, most emphasis has been placed on investigation of sandy deposits. There has been no production of hydrocarbons from post-Eocene sediments on the Norwegian continental shelf. One medium-sized gas discovery in Pleistocene glacial sand deposits (upper part of the Nordland Group) was made in wells 35/2-1 and 35/2-2, several small gas discoveries have been reported from the Vade Formation (wells 2/2-1, 2/2-2 and 2/3-1), and the Utsira Formation (well 15/6-9 S). Oil has been discovered in the lower Nordland Group (well 1/5-3 S) and in a sandy section just below the Skade Formation in well 25/2-10 S. Shallow gas and oil shows are recorded in a number of wells, e.g. before placing the Gullfaks Field platform (northern North Sea, block 34/10) shallow gas was discovered in a number of wells in the Late Pliocene Nordland Group (NPD 2013). The high oil price in recent years has resulted in an increased focus on high-risk exploration targets, including post-Eocene sandy formations and units.

To meet Norway’s commitment to the Kyoto agreement on reduction of greenhouse gas emissions, it has been suggested to separate and store CO2 from large point sources. Depleted oil and gas fields could be used for CO2 storage, but their capacity will be too small if carbon capture and storage (CCS) will be utilised as a major instrument to prevent global climate warming. There exists a very large potential storage capacity in post-Eocene saline aquifers on the Norwegian continental shelf, especially in the Utsira Formation in the North Sea. CCS has been implemented full scale at the Sleipner gas field (North Sea, block 15/12), where one million tons of CO2 per year have been successfully injected into the Utsira Formation since 1996. Currently, the Utsira Formation has also been used in other fields for the production of water for injection, and the injection of produced water and other waste like drill cuttings and chemicals. The post-Eocene deposits on the Norwegian continental shelf have been far less sampled and investigated than the older sediments, which have been the main target for hydrocarbon exploration. However, when drilling exploration wells the oil companies commonly sample the post-Eocene deposits with drill cuttings, except for the upper part of the Pleistocene. The sampling programme is usually considerably less dense than in the deeper section, e.g. every ten metres compared to every three metres in reservoir sections. A small number of wells have been sampled with sidewall cores and short conventional cores. The conventional cores are used mainly for geotechnical investigations. Contracted biostratigraphical consultants usually execute routine investigations, but the samples are often investigated with a large sample spacing and only limited effort is put into the analyses. Mistakes and inaccuracies in the biostratigraphical analysis and age interpretations have led to errors in completion logs, final well reports, regional seismic mapping and even in the stratigraphic nomenclature. Historically, this has led to considerable confusion in our understanding of the overall stratigraphy. Several scientific investigations have tried to improve this situation, including those of Gregersen (1998), Gregersen & Johannessen (2007), Gregersen et al. (1997), Henriksen et al. (2005), Jarsve et al. (work in progress), Jordt et al. (1995, 2000), Løseth & Henriksen (2005), Martinsen et al. (1999), Michelsen & Danielsen (1996), Michelsen et al. (1995) and Ryseth et al. (2003). Much of their work has focused on regional seismic interpretation, but some of their correlations have unfortunately been hampered by inaccurate/incorrect completion logs and final well reports. Biostratigraphic studies, including the present paper, dealing with re-dating of petroleum wells and boreholes may improve this situation. Regional seismic studies dealing with the outer shelf, continental slope and rise, including Laberg et al. (2001, 2005a and b), Stoker et al. (2005a and b) and Knies et al. (2009), are less affected by this problem since their seismic data, to a large extent, are calibrated with data from deep-sea ODP/DSDP boreholes.

In Jutland, Denmark, upper Paleogene and Neogene sediments occur below the glacial deposits over large areas. According to Dybkjær & Piasecki (2008), most of the water used in private households, in industry and for irrigation in Denmark comes from subsurface aquifers. Some of the most important aquifers in Jutland (Jylland in Danish), western Denmark, are sand layers deposited in the early Neogene (Early to Middle Miocene). Global climatic variations and major sea-level changes (Zachos et al. 2001), combined with uplift of the southern part of the Fennoscandian Shield, led to increased sediment transport from the north (present-day Finland, Sweden and particularly Norway, Map 1). This resulted in deposition of huge, fluvio-deltaic sand systems intercalated with marine clay (Rasmussen 2004). According to Rasmussen et al. (2004), the Geological Survey of Denmark and Greenland (GEUS) has executed a systematic study of these deposits, which includes detailed sedimentological descriptions of outcrops, sedimentological and log-interpretations of new stratigraphic boreholes and interpretation of high-resolution seismic data. More than 50 boreholes and outcrops (including some offshore boreholes) have been studied palynologically. These studies have resulted in a dinoflagellate cyst zonation scheme (Dybkjær & Piasecki 2008, 2010) and a regional, stratigraphic model. In many of these sites, thin-walled calcareous foraminifera have been dissolved due to a high concentration of humic acid in the pore water. However, based on examination of the foraminiferal contents in marine clay from 18 onshore boreholes (most from the North German Basin in the southern Jutland), Laursen & Kristoffersen (1999) have established a detailed foraminiferal biostratigraphy of the Miocene Ribe and Måde groups for these areas.

To facilitate correlation of the Danish onshore boreholes and outcrops (palynologically investigated by Dybkjær & Piasecki, 2008 and 2010) with the Norwegian wells and boreholes, a large number of the Danish samples containing molluscs and mollusc fragments have been analysed for Sr isotopes. The thick-walled tests of molluscs are far less prone to dissolution than the foraminiferal tests and are present in many samples where foraminifera are absent. The detailed results from this investigation will be published in Eidvin et al. (work in progress a and b), but the main results are shown here in Link to Danish Sr isotope ages.

In the present publication, all absolute ages are referred to Berggren et al. (1995). The main reason for this is that the Strontium Isotope Stratigraphy (SIS) Look-up table of Howard & McArthur (1997) has been used, and this is based on the time scale of Berggren et al. (1995). For the post-Eocene part, this time scale does not deviate to any great extent from the new time scale of the International Commission on Stratigraphy (ICS 2013). The most important difference is that the base Pleistocene has been moved from 1.85 Ma to 2.588 Ma (see Table 1). All depths are expressed as metres below the rig floor (m RKB) if not stated otherwise.

In the current publication, all the well, borehole and outcrop descriptions are hyperlinked to the numbers on Map 1, Map 2 and the numbers and columns on Fig. 1 and Fig. 2. Seismic profiles are linked to the profile numbers. The well, borehole and outcrop information includes figures and descriptions of lithology, gamma logs, lithostratigraphic units, fossil units, paleobathymetry, Sr isotope analyses and sample types. All microfossil assemblages and zones are described and included in the figures, but no fossil range charts are included. Many range charts of the most stratigraphically important taxa can be found in our cited papers. However, in the future we plan to make full range charts available on DVD on request. For a discussion of the interpretation of paleobathymetry, we refer the reader to our previous papers (see above). The definition of bathymetric zones is according to van Hinte (1978); inner neritic: 0-30 m, middle neritic: 30-100 m, outer neritic: 100-200 m and upper bathyal: 200-600 m.