Geological Survey of Denmark and Greenland Bulletin 12, 16-23 16 core samples have been available. As the use of stratigraphic lowest occurrences (LO) of taxa in cuttings samples may be hampered due to downhole caving, the event succes- sion comprises almost exclusively stratigraphic highest occurrences (HO) of taxa (a single significant LO is in- cluded in the succession). The event succession is shown in Fig. 5a–c; its correlation with international and North Sea biozones is shown in Fig. 6a–c. Seismic sections from the 2-D and 3-D seismic surveys CGD85, DK-1, RTD81–RE94, UCG96 and UCGE97 have been used to further support the well correlation and to map the stratigraphic units in areas with only scattered well coverage. The combined results from the correlation and mapping procedures are presented as isochore maps for individual stratigraphic units. Inspection of cuttings samples from 16 key wells sup- plemented with sedimentological studies of cored inter- vals from 23 wells have formed the basis for the litholog- ical and sedimentological descriptions of the units. The well depths mentioned in the lithostratigraphy sec- tion are loggers’ depths measured either from rotary table (MDRT) or kelly bushing (MDKB). Supplementary data for new type and reference wells are provided in Table 1. The names assigned to the new lithostratigraphic units defined herein are derived from Nordic mythology and thus follow the nomenclatural tradition previously established for the Norwegian North Sea (Isaksen & Tonstad 1989). It should be noted that the micropalaeontology-based palaeoenvironmental terminology used herein was origi- nally developed for a passive margin situation (e.g. the terms ‘neritic’ and ‘bathyal’ to indicate the physiographic zones ‘shelf ’ and ‘shelf- slope’, respectively). Its application herein to the epicontinental North Sea Basin solely relates to depositional depth. Offshore and onshore lithostratigraphic nomenclature There is a high degree of lithological similarity between the Palaeogene–Neogene mudstone succession in Danish offshore boreholes and that in onshore exposures and bore- holes. However, the status of the Danish onshore units is quite varied since many units were named before a stan- dard for description of a lithostratigraphic unit was estab- lished; some fulfil these requirements, whereas others are still informal. If a previously established onshore unit and an offshore unit can be demonstrated to be identical (e.g. the Holmehus Formation and the new Ve Member pro- posed herein), the name of the onshore unit theoretically has priority over the name of the offshore unit (Salvador 1994). In other cases, names of offshore units can be ar- gued to have priority over onshore units (e.g. Sele and Balder Formations over Ølst Formation). However, in order to acknowledge the traditional distinction between offshore and onshore stratigraphic nomenclature, the two sets of nomenclature are kept separate herein. Whenever possible, comments are given in the text to explain the relationship between offshore and onshore Danish strati- graphic nomenclature. A correlation between the two sets of nomenclature is shown in Fig. 2. Chronostratigraphy and biostratigraphy Age assessment of the lithostratigraphic units in the North Sea sedimentary succession is based on correlation between key biostratigraphic events encountered in the units and the calibrated standard chronostratigraphy published by Berggren et al. (1995), with modification for the Pale- ocene–Eocene boundary following ratification of its posi- tion by the International Union of Geological Scientists (Aubry et al. 2002). The key events are from biostrati- graphic zonation schemes established for the North Sea area. Planktonic and benthic microfossils are covered by the zonation schemes of King (1983, 1989; Figs 5a–c, 6a–c). Dinoflagellates from the Paleocene and Eocene Epochs are covered by the zonation scheme of Mudge & Bujak (1996b; Fig. 6a, b); the Oligocene and Miocene Epochs are covered by the zonation schemes of Costa & Manum (1988) with modifications by Köthe (1990, 2003; Fig. 6b, c). Key events from these schemes used in this study are listed in Fig. 5a–c. For the dinoflagellate events, geochronological calibra- tion has been largely established using age estimates from Hardenbol et al. (1998), Munsterman & Brinkhuis (2004) and Williams et al. (2004). For events not mentioned in these three publications, the works of Mudge & Bujak 17 P2 P9 P7 P6 b a P5 P4 c P8 NP13 NP12 NP10 NP9 NP11 b a b a P3 c b a P1 Pα + P0 NP8 NP6 NP5 NP4 NP3 NP2 NP1 NP7 Abathom- phalus mayaroensis CC26 CC25 (pars) Pseudotextularia elegans P6 P5 P4 P3 P2 P1 E1a E2a E2b E2c E3a E3b L E1c E1bE o ce ne ( pa rs ) Pa le o ce ne C re ta ce o us (p ar s) NP14 (pars) E3c 50 60 55 65 NSP6 (pars) NSP5b NSP4 NSB4 (pars) NSB3a NSB2 NSP5a NSB3b NSP3 NSP2 NSP1 NSB1 65.0 Ypresian (pars) Lo w er ( pa rs ) U pp er Lo w er 55.5 60.0 Thanetian Selandian Danian U pp er ( pa rs ) Maastrichtian (pars) 57.9 54.5 Sparnacian c b a b c a Planktonic microfossils Benthic microfossils Dinoflagellate cysts Planktonic microfossils Calcareous nannofossils North Sea biozonesStandard biozones Chronostratigraphy (Berggren et al. 1995) StageSeries Berggren & Miller (1988), Berggren et al. (1995) Mudge & Bujak (1996b) Martini (1971) King (1989) Geo- chronology Ma a Fig. 6. Biostratigraphic correlation charts showing approximate correlation of calibrated standard planktonic foraminifer and nannofossil bio- zones with North Sea microfossil and dinoflagellate biozones. Calibration of the standard biozones follows Hardenbol et al. (1998). Relationships between the North Sea biozones are approximate and their correlation with the standard zones may deviate from that of the original authors (for discussion, see text). a: Paleocene–Eocene biostratigraphic correlation chart. b: Eocene–Oligocene biostratigraphic correlation chart. c: Oli- gocene – Middle Miocene biostratigraphic correlation chart. P17 E6b NP14 P9 P7 P8 NP13 NP12 NP11 E2a E2b E2c E3a E3b E1c E1b E3c NSP6 NSP5b NSB4 NSB3aNSP5a NSB3b P18 P16 P15 Np23 (pars) NP22 NP21 NP19–20 NP18 P14 P12 P11 P10 P13 NP17 NP16 NP15 E3d E4a E4b E4c E4d E5a E5b E6a E6c E7a E7b E8b E8a D13 Mudge & Bujak (1996b) Costa & Manum (1988), Köthe (1990) Planktonic microfossils Benthic microfossils Dinoflagellate cysts Planktonic microfossils Calcareous nannofossils North Sea biozonesStandard biozones P19 (pars) 35 40 50 45 O lig o ce ne (p ar s) Lo w er ( pa rs ) Eo ce ne ( pa rs ) U pp er M id dl e Lo w er ( pa rs ) NSB7aNSP9b NSP9a NSB6b NSP8c NSB6a NSP8b NSB5c NSP8a NSP7 NSB5b NSB5a P6 b a Np10 (pars) NSP4 (pars) NSB2 (pars) E1a (pars) Geo- chronology Ma Chronostratigraphy (Berggren et al. 1995) StageSeries Berggren & Miller (1988), Berggren et al. (1995) Costa & Manum (1988), Köthe (1990), Mudge & Bujak (1996b) Martini (1971) King (1989) Rupelian (pars) Priabonian 41.3 Lutetian Ypresian (pars) 49.0 37.0 33.7 Bartonian b Fig. 6b. Eocene–Oligocene biostratigraphic correlation chart. 18 M7 M9 M12 M8 M11M10 M6 M5 M3 M2 M4 M1 b a P22 P21 b a P20 P19 P18 NN5 NN6 NN9A– NN7 NN4 NN3 NN2 NN1 NP25 NP24 NP23 NP22 NP21 (pars) D13 D14 D15 D16 D17 D18 D19 Tortonian (pars) Burdigalian Aquitanian M io ce ne ( pa rs ) Lo w er Chattian U pp er Rupelian (pars) Lo w er ( pa rs ) O lig o ce ne ( pa rs ) M id dl e Langhian Serravallian 28.5 23.8 20.5 16.4 14.8 11.2 15 20 30 25 U pp er (p ar s) NSP9a (pars) NSB6b (pars) NSP14b NSB13a NSP14a NSB12c NSP13 NSB12b NSB12a NSP12 NSB11 NSP11 NSP10 NSB10 NSB9 NSP9c NSB8c NSB8b NSB8a NSB7b NSB7a NSP9b M13a (pars) NN9b (pars) Planktonic microfossils Benthic microfossils Dinoflagellate cysts Planktonic microfossils Calcareous nannofossils North Sea biozonesStandard biozones Chronostratigraphy (Berggren et al. 1995) StageSeries Berggren & Miller (1988), Berggren et al. (1995) Costa & Manum (1988), Köthe (1990), Martini (1971) King (1989) Geo- chronology Ma c Fig. 6c. Oligocene – Middle Miocene biostratigraphic correlation chart. 19 20 (1996b), Dybkjær (2004), Piasecki (2005) and Schiøler (2005) have been consulted. However, whereas Harden- bol et al. (1998) and Williams et al. (2004) used the time- scale of Berggren et al. (1995), Mudge & Bujak used the slightly older timescale from Haq et al. (1987) for cali- bration of their events. Therefore, the ages of events only listed by Mudge & Bujak have been recalibrated herein to conform to the timescale of Berggren et al. (1995). King (1989) calibrated his planktonic and benthic mi- crofossil zone markers with the standard chronostrati- graphic scale of Berggren et al. (1985a, b). However, King noted that only a few first-order correlations were possi- ble; most of the calibrations were made using dinoflagel- lates, planktonic foraminifers and nannoplankton from onshore sections in the North Sea Basin (King 1989 p. 420); the correlation of the Lower Miocene is particularly uncertain (King 1989 p. 446). Paleocene and Eocene key planktonic and benthic microfossil events from King (1989) were subsequently correlated with the North Sea dinoflagellate events by Mudge & Bujak (1996b). By using the above-mentioned recalibration of key dinoflagellate events from Mudge & Bujak (1996b), it is feasible to in- directly correlate King’s North Sea microfossil events with the timescale of Berggren et al. (1995). This has been at- tempted in Fig. 5a–c. Figure 6a–c shows the relationships between the North Sea biozones and their correlation with the standard plank- tonic foraminifer and calcareous nannofossil zones. How- ever, it should be noticed that in a few cases the correla- tion of the North Sea microfossil and dinoflagellate zones with the standard zones in Fig. 6a–c is at variance with that of the authors of the same zones. This is an effect of improved age determinations of the standard zones and the dinoflagellate events used to calibrate the North Sea microfossil zones. The section below outlines the current status for the Palaeogene and Neogene chronostratigraphic units covered by the studied succession and lists key biostratigraphic events used for chronostratigraphic correlation of the succession. Paleocene The bases of the Selandian and Thanetian Stages, which together constitute the Upper Paleocene Series, have yet to be formally defined. However, ongoing work in the International Subcommission on Palaeogene Stratigraphy indicates that the Global Standard Stratotype-section and Point (GSSP) of the base of the Selandian Stage will prob- ably be close to the P2–P3a or the P3a–P3b standard planktonic foraminifer zone boundary, while the GSSP for the Thanetian Stage will probably be at the base of Magnetochron C26n (Gradstein & Ogg 2002). Harden- bol et al. (1998) followed Berggren et al. (1995) in plac- ing the base of the Selandian Stage at the base of Zone P3a, at the lowest occurrence of the planktonic foramini- fer Morozovella angulata. However, many of the micro- fossil species that characterise the Danian–Selandian boun- dary interval in the international zonation schemes, in- cluding M. angulata, are extremely rare or absent in the North Sea Basin thereby hampering chronostratigraphic correlation of the boundary. Based on a study of core material from the type area for the Danian and Selandian Stages, Clemmensen & Thomsen (2005) concluded that the Danian–Selandian stage boundary is located in the upper part of the NP4 standard nannofossil zone, close to the NP4–NP5 zone boundary, approximately at the P3a– P3b zone boundary, at c. 60 Ma on the timescale of Hard- enbol et al. (1998). They further concluded that there is a hiatus between the Danian and Selandian Stages in the Danish area outside the Central Graben due to trunca- tion of the Danian limestones of the Ekofisk Formation (Fig. 5a; Clemmensen & Thomsen 2005). Hence, the Danian–Selandian stage boundary is herein placed just below the downhole reappearance (provisional HO) of planktonic foraminifers and the HO of the dinoflagellate Alisocysta reticulata, but above the closely spaced events marked by the HO of the planktonic foraminifers Sub- botina trivialis and Globanomalina cf. compressa (e.g. Jones 1999; Mudge & Bujak 2001). The Selandian–Thanetian stage boundary is herein approximated by the HO of the dinoflagellate Palaeope- ridinium pyrophorum, at the base of the P5 dinoflagellate Zone of Mudge & Bujak (1996b). This level is close to the base of Magnetochron C26n, according to Harden- bol et al. (1998). Eocene The base of the Eocene is at the base of the negative car- bon isotope excursion (CIE) at 55.5 Ma (Berggren & Aubry 1996; Aubry et al. 2002). This position is below the base of the Ypresian Stage, the lowermost Eocene Stage. Therefore it has been proposed to reintroduce the Spar- nacian Stage as the new basal Eocene Stage between the CIE and the base of the Ypresian (Aubry et al. 2003). The CIE has been correlated with the proliferation of the dino- flagellate genus Apectodinium, an event recognised glo- bally (e.g. Knox 1996; Crouch et al. 2001). Onshore Den- mark, the CIE and the proliferation of Apectodinium coin- cides precisely with the laminated Stolle Klint Clay in the 21 2900 m 3000 2900 m 3000 2000 m 2100 2700 m 2900 m Horda Fm Balder Fm Sele Fm Lista Fm Bue Mb R o ga la nd G ro up St ro ns ay G ro up Ve Mb Vile Mb Våle Fm Chalk Group 3000 2800 Kim-1 GR Sonic GR Sonic GR Sonic GR Sonic GR Sonic Kim-1 Mona-1 Cleo-1 Gulnare-1 E-8 E-8 lowermost part of the Haslund Member of the Ølst For- mation (Heilmann-Clausen & Schmitz 2000; Willum- sen 2004). In the North Sea Basin, the acme of Apectodin- ium is located in the lowermost, laminated part of the Sele Formation (sensu Deegan & Scull 1977, see below) according to Knox (1996). As the event is a LO, its posi- tion cannot be determined with certainty in wells in which this interval is covered only by cuttings samples. In the North Sea Basin, however, this stratigraphic level is char- acterised by a prominent excursion on the gamma-ray log near the base of the Sele Formation which therefore can be used as an approximation for the base of the Eocene Series. The remaining stages of the Eocene Series, the Ypre- sian, Lutetian, Bartonian and Priabonian Stages, lack ba- sal boundary GSSPs for the present. In this paper, we fol- low Mudge & Bujak (1996b) and approximate the bases of the three latter stages by using three key dinoflagellate events: the base of the Lutetian Stage is at the HO of common Eatonicysta ursulae, the base of the Bartonian Stage is close to the HO of Diphyes colligerum, and the base of the Priabonian Stage is close to the HO of Heter- aulacacysta porosa. The base of the classic Ypresian Stage is at the LO of the calcareous nannoplankton species Tri- brachiatus digitalis. As yet, there is no commonly recog- nised HO index event at that level in the North Sea Ba- sin, but the boundary between the Sparnacian and the Ypresian Stages may be placed below the HOs of com- mon Cerodinium wardenense and Apectodinium augustum (Fig. 5a), both dinoflagellate species. Oligocene The GSSP for the Eocene–Oligocene boundary is in the Massignano section (central Italy), at the highest occur- rence of the planktonic foraminifer genera Hantkenina and Cribrohantkenina, immediately above the P17–P18 plank- tonic foraminifer zone boundary (Premoli Silva & Jenkins 1993). However, hantkeninids have not been observed from the North Sea Basin and alternative zone markers have therefore been used here. In the North Sea Basin, the planktonic foraminifer Globigerinatheka index and the benthic foraminifer Cibicidoides truncanus have their HOs in the uppermost Eocene (King 1989), and the two events may be used to approximate the Eocene–Oligocene bound- ary. A palynological marker of the lowermost Oligocene is the HO of the dinoflagellate Areosphaeridium diktyo- plokum (Brinkhuis & Biffi 1993; Brinkhuis & Visscher 1995), which is widespread in the North Sea Basin. The three latter events in combination serve as useful markers for bracketing the Eocene–Oligocene boundary in the North Sea Basin. The principal criterion for the Rupelian–Chattian (Lower–Upper Oligocene) boundary has not yet been de- Fig. 7. Log panel illustrating the thickness variation of the Rogaland Group formations in the Danish Central Graben. 22 cided by the Subcommission on Palaeogene Stratigraphy. Indications are that the boundary may be positioned at the base of the P21b planktonic foraminifer zone (Premoli Silva 2005), at 28.5 Ma (Hardenbol et al. 1998). How- ever, the defining boundary event cannot be recognised in the North Sea Basin and its exact correlation with the North Sea biostratigraphic event succession remains un- certain. Instead, most North Sea biostratigraphers recog- nise the Rupelian–Chattian stage boundary at the HO of the benthic foraminifer Rotaliatina bulimoides. This event marks the top of the NSB7 Zone of King (1983, 1989; Fig. 5c) and the NSR7 Zone of Gradstein et al. (1994). The HO of R. bulimoides is at 29 Ma in the northern North Sea according to Gradstein & Bäckström (1996), slightly older than the 28.5 Ma for the Rupelian–Chat- tian stage boundary quoted by Hardenbol et al. (1998). The Rupelian–Chattian stage boundary may also be ap- proximated by the HO of the dinoflagellate Rhombodin- ium draco. In the North Sea wells reported herein, where both the HOs of R. bulimoides and R. draco have been recorded, these events are largely contemporaneous. How- ever, in the type area of the Rupelian and Chattian Stages, R. draco has its HO above R. bulimoides in the type Chat- tian (van Simaeys et al. 2004). Therefore, it may be infer- red that the two latter events probably bracket the Rupe- lian–Chattian boundary (Fig. 5c). Ve Mb Tyr Mb Bue Mb Log depth Core depth Våle Fm Lista Fm Bor Mb GR Soni c Cecilie-1 clay si. vf. f. m. Sand c. vc. P P P P P P P P P ? S 5o 2240 2250 2260 2270 2280 2240 2250 2260 2270 2280 Vile Mb Fig. 8. Core log showing intrusive sand- stones in the Våle and Lista Formations in the Cecilie-1 well. For legend, see Fig. 9. The two intervals marked by grey bars in the core depth column are shown as core photographs in Fig. 10. 23 Lithology Sedimentary structures Sandstone intrusions Mudstone clasts Chert Siderite Calcite concretions Trace fossils Sandstone Mudstone Marl Chalk Carbonate cement (non-calcitic) Calcite cement Pyrite Glaucony Parallel lamination Faint parallel lamination Water-escape pipes (large) Load cast Dish structures and pipes Deformed/slumped bedding Fractures/faults Bed boundary Cross-lamination Sandstone intrusions Flow structures Stylolites Zoophycos Helminthopsis Planolites Thalassinoides Chondrites Low Moderate Intense Degree of bioturbation P G S C Miocene The Oligocene–Miocene Series boundary is bracketed by a number of HOs at its type section (Lemme-Carosio, north-west Italy). Unfortunately, none of the foraminifer events are believed to be true stratigraphic tops (facies de- pendent), and reworking in the section hampers the use of nannofossil tops (Steininger et al. 1997). However, the dinoflagellate succession from the Lemme-Carosio section has been documented in detail by Powell (1986), Brinkhuis et al. (1992) and Zevenboom (1995, 1996), and provides a means for direct correlation to the North Sea Basin (Munsterman & Brinkhuis 2004). The HO of Distato- dinium biffii is below the Chattian–Aquitanian boundary in its type section and the HO of Chiropteridium spp. is above. This succession of events can be recognised in many North Sea wells, and the Chattian–Aquitanian boundary is positioned between the two. Supporting microfossil events that characterise the lowermost Miocene include the HO of the diatom Aulacodiscus insignis quadrata (small morphotype, same as diatom sp. 3 of King 1983, 1989), a widespread event in the North Sea Basin, and the HO of the benthic foraminifer Brizalina antiqua (King 1989). The HO of the planktonic foraminifer Paragloborotalia nana marks uppermost Chattian strata. The principal criteria for the Aquitanian–Burdigalian, Burdigalian–Langhian and Langhian–Serravallian stage boundaries are as yet undecided. Most authors place the three boundaries at microfossil zone boundaries or mag- netochron boundaries at 20.5, 16.4 and 14.8 Ma, respec- tively (Hardenbol et al. 1998; Williams et al. 2004). The correlation of the three boundaries to the North Sea Ba- sin is feasible using the dinoflagellate zonation scheme of De Verteuil & Norris (1996), established for US East Coast sections and the review of dinoflagellate index events pub- lished by Williams et al. (2004). The former zonation scheme is correlated directly with the zonation schemes of Berggren et al. (1995) and the Miocene timescale by means of calcareous nannofossils and foraminifers. The Aquitanian–Burdigalian boundary is positioned just above the HO of the dinoflagellate Caligodinium amiculum. The Burdigalian–Langhian boundary is placed between the HO of the dinoflagellates Hystrichokolpoma cinctum and Pyxidinopsis fairhavenensis, two events that bracket the boundary level. The Langhian–Serravallian boundary is slightly above the HO of the dinoflagellate Cousteaudi- nium aubryae. In this study, these four events have been used to approximate the three stage boundaries. Fig. 9. Legend for core logs (Figs. 8, 11, 18, 27, 30 and 39); the lithological colour scheme is also adopted on well sections (e.g. Fig. 13).