Geological Survey of Denmark and Greenland Bulletin 26, 2012,13-16 13 Geology of the Femern Bælt area between Denmark and Germany Emma Sheldon, Peter Gravesen and Henrik Nøhr-Hansen Geological and geotechnical investigations in the Femern Bælt area were undertaken from 1995 to 2010 (Rambøll Arup JV 2011) in preparation for the fixed link between Lol- land in Denmark and Fehmarn in Germany. As a result, new data have been acquired on the stratigraphy and distribution of the deposits and the major structures and tectonic influ- ence on the layers close to the surface. Previous investigations of Cretaceous–Palaeogene deposits on southern Lolland (Fig.  1) were limited due to lack of outcrops and borehole data. Two deep boreholes and geophysical surveys (1952– 1953) revealed: (1) the presence of a salt diapir at Rødbyhavn, (2) upper Maastrichtian chalk 29–143 m below Quaternary deposits and (3) an erosional window in the Palaeogene cov- er. Boreholes to the east of Rødbyhavn (1992–1994) revealed the sediment distribution on southern Lolland and showed that Cretaceous and Palaeogene deposits are cut by several NW–SE-orientated faults. This paper presents a summary of lithostratigraphic and biostratigraphic investigations and a brief description of the geological development in the area. Methods A multidisciplinary biostratigraphic study was undertaken of 170 samples from 46 wells drilled in 2009–2010 in the Femern Bælt region. The wells were drilled to depths of 50– 100 m and were fully cored in the pre-Quaternary deposits. One to ten samples from each well were selected for biostrati- graphic analysis by Rambøll Arup JV. Nannofossil analysis was carried out on all samples. Supplementary analyses were carried out using microfossils and dinoflagellate cysts (dino- cysts) when necessary. Nannofossils are particularly useful for dating chalk and clay, microfossils for chalk, sand and clay and dinocysts for clay. The use of three fossil groups al- lowed for well-constrained and reliable dating and formation identification (Sheldon & Nøhr-Hansen 2010). In addition, 13 samples from DGU core 241.213, a water well from 2011 on Lolland, were analysed. Biostratigraphy and lithostratigraphy A chronostratigraphic, biostratigraphic and lithostratigraph- ic correlation is presented in Fig. 2. The lithologies and se- lected marker fossils reported in this article are as follows (see also Fig. 3): Tor Formation equivalent (Campanian–Maastrichtian) – The Tor Formation of the North Sea was originally de- scribed by Deegan & Scull (1977) as homogeneous white or grey chalk, bioturbated pelagic chalk, laminated chalk and redeposited chalk. The Femern Bælt area chalk is slightly in- durated, with <5% flint nodules. Biostratigraphic marker fossils: Tranolithus orionatus, Reinhardtites levis, Nephrolithus frequens, Arkhangelskiella maastrichtiana, Eiffellithus turriseiffelii, Prediscosphaera spinosa, Cribrosphaerella daniae (nannofossils), Bolivinoides laevigatus, Praebulimina levis, Reusella szajnochae szajno- chae, Bolivina incrassata, Stensioeina pommerana (foraminif- era), Cannosphaeropsis utinensis, Montanarocysta aemiliana and Xenascus wetzelii (dinocysts). Danian limestone (lower–middle Danian) – comprises fossil- iferous limestone, rich in echinoderm, bryozoan and bivalve fragments and is recognised as a thin layer on Lolland (DGU core 241.213). Biostratigraphic marker fossils: Prinsius tenuiculus, Prin- sius dimorphosus, Chiasmolithus danicus, Cruciplacolithus tenuis, Neochiastozygus modestus (nannofossils), Eoglobige- Fig. 1. A: Map of Denmark and northern Germany showing the proposed location of the fixed link across the Femern Bælt. B: Geological map of the Femern Bælt region (after Håkansson & Pedersen 1992). Lolland Fehmarn Femern Bælt Rødbyhavn Eocene Paleocene (without Danian) Danian Upper Cretaceous Ringkøbing–Fyn High 100 km 14°E 57°N 55° SwedenDenmark Germany German Basin Danish Basin A B DGU 241.213 Norway © 2012 GEUS. Geological Survey of Denmark and Greenland Bulletin 26, 13–16. Open access: www.geus.dk/publications/bull 1414 rina edita, Globoconusa daubjergensis and Cibicidoides suc- cedens (foraminifera). Lellinge Greensand (lower Selandian) – In DGU core 241.213, Lellinge Greensand (originally described by Gry 1935) comprises olive-grey, glauconitic, sandy, hard lime- stone intercalated with fine-grained clay with brown phos- phate nodules and pyrite. Lellinge Greensand is also encoun- tered in a number of Femern Bælt boreholes. Biostratigraphic marker fossils: common Neochiastozygus perfectus and Prinsius martinii (nannofossils), Globanomali- na ehrenbergi, Bulimina trigonalis (common) and Gavelinel- la danica (foraminifera) with reworked Danian and Upper Cretaceous nanno- and microfossils (Danian limestone and Tor Formation equivalent) and macrofossil debris. Æbelø Formation (middle Selandian) – The Æbelø Forma- tion (Heilmann-Clausen et al. 1985) comprises slightly cal- careous to non-calcareous, silty – very silty, grey clay. Biostratigraphic marker fossils: Chiasmolithus edentulus, Chiasmolithus eograndis (nannofossils), Isabelidinium? vi- borgense and Palaeoperidinium pyrophorum (dinocysts). Holmehus Formation (Selandian–Thanetian) – The Holme- hus Formation (Heilmann-Clausen et al. 1985) consists of non-calcareous, greenish, brownish and reddish, very fine- grained clay with minor sand and phosphatic or sideritic concretions. Biostratigraphic marker fossils: Transversopontis pulcher- oides, Zygodiscus adamas, Neococcolithes protenus (nannofos- sils), Cyclammina amplectens, (foraminifera), Alisocysta sp. 1 Heilmann-Clausen 1985 and Cerodinium medcalfii (dino- cysts). Ølst Formation (lower Ypresian) – The Ølst Formation (Heilmann-Clausen et al. 1985) is a grey to almost black, sandy, silty and mainly non-calcareous clay, interbedded with layers and laminae of black or grey volcanic ash. Biostratigraphic marker fossils: Sphenolithus editus, Tri- brachiatus orthostylus, Lophodolithus nascens (nannofossils), Fenestrella antiqua, Coscinodiscus morsianus moelleri, Tri- ceratium spp. (diatoms), Apectodinium hyperacanthum and Deflandrea oebisfeldensis (dinocysts). Røsnæs Clay Formation (middle Ypresian) – The Røsnæs Clay Formation (Dinesen et al. 1977; Heilmann-Clausen et al. 1985) comprises red, brown and yellow-brown, very fine- grained, plastic marine clay with glauconitic beds at the base and greenish volcanic ash layers throughout. Fig. 2. Chrono-, bio- and lithostratigraphy of the Campanian–Eocene in Denmark. Note, not all formations have been found in the investigated area. NP14 NP15 (pars) NP10 49.0 E o ce n e NP13 NP12 NP9 NP11 NP8 NP6 NP5 NP4 NP3 NP2 NP1 NP7 NNTe 8 (pars) NNTe 7 NNTe 1 NNTe 2 NNTp 4 NNTp 3 NNTp 1 UC16–20 NNTp 2 NNTp 9 NNTp 10 N O T Z O N E D 8 7 5 6 6 5 4 3 Lillebælt Clay Fm L2 Fur Fm Ølst Fm Stolle Klint Clay Øster- rende Clay Holmehus Fm Æbelø Fm Danian Lime- stone Tor Fm equiv. Denmark onshore Kerteminde Marl Lellinge GreensandP al eo ce n e 60 55 65 65.0 Ypresian L o w er M id d le U p p er L o w er 55.5 60.0 Selandian 57.9 54.5 C re t. U . 50 Lutetian Sparnacian Thanetian Maastrichtian Danian Campanian/ Røsnæs Clay Fm R5/R6 D6a / D6b upper D9 lower D9 D8 D7a D7b D5b D5a D4 Viborg zone 7 Viborg zone 6 Viborg zone 5 Viborg zone 4 Viborg zone 3 Viborg zone 2 Knudsh. Mb. Røsnæs Clay Fm R5/R4 L1 R6 R1 H ei lm an n - C la u se n ( 1 9 8 5 ) H ei lm an n - C la u se n & C o st a (1 9 8 9 ) Martini (1971) North Sea biozones Standard biozones Chrono- stratigraphy Litho- strat. Danish biozones Calcareous nannofossils Varol (1998) Burnett (1998) Dinoflagellate cysts Berggren et al. (1995) StageSeries A ge ( M a) Calcareous nannofossils 15 Biostratigraphic marker fossils: Discoaster kuepperi, Im- periaster obscurus, Toweius occulatus, Rhabdosphaera pin- guis, Discoaster lodoensis (nannofossils), Turrilina brevispira, Clavulina anglica, Pseudohastigerina wilcoxensis, Gaudryina hiltermanni, Subbotina patagonica (foraminifera), Dracod- inium? condylos, Ochetodinium romanum, Wetzeliella astra, Dracodinium solidum, Eatonicysta ursulae and Dracodinium varielongitudum (dinocysts). Lillebælt Clay Formation (upper Ypresian – lower Lutetian) – The Lillebælt Clay Formation is a green-grey, non-calcar- eous, very fine-grained plastic clay containing concretions, with red-brown clay beds in the lower part (Dinesen et al. 1977; Heilmann-Clausen et al. 1985). Biostratigraphic marker fossils: Vaginulinopsis decoratus (foraminifera), Membranilarnacia compressa, Charlesdown- iea columna and Eatonicysta furensis (dinocysts). Geological development Lolland is located to the south of the Ringkøbing–Fyn High, in the German Basin. During the Late Cretaceaous, fully marine conditions characterised the Danish area including the northern highs and chalk of the Campanian – upper Maastrichtian Tor Formation equivalent was deposited. Da- nian limestone and Lellinge Greensand have recently been found in situ on southern Lolland and are documented here for the first time. The Danian limestone is c. 2 m thick. Da- nian nannofosssils and microfossils are also found in small limestone clasts within the Selandian deposits, indicating that Danian sediments were eroded and partially redepos- ited at the end of the Danian and probably also in the earliest Selandian. The lower Selandian glauconitic and conglomeratic de- posits of the Lellinge Greensand rest on Danian sediments on Sjælland, especially in the Copenhagen area (Stouge et al. 2000). Clasts, microfossils and nannofossils from the lower Selandian also indicate deposits from the Lellinge Greensand in the Femern Bælt area. The Lellinge Greensand is at least 12–13 m thick; the top is eroded and covered by Quaternary deposits. In DGU core 241.213 the Lellinge Greensand is found 138 m below ground surface. The encountered glauco- nitic deposits from the Lelllinge Greensand rest on Danian limestone in a small subsided fault block, demonstrating that the lowermost Selandian was probably deposited in the area and subsequently eroded. The early–middle Paleocene sea was more restricted than in the Cretaceous and several highs bordered the marine area (Clausen & Huuse 2002). The Danian was dominated by erosion, rising sea level characterised the early Selandian and erosion dominated again during the late early Selandian. These two erosional episodes may have resulted in sediment removal, but it is also possible that the area was subaerial during part of the Danian–Selandian. Continued erosion or nondeposition characterised the upper Selandian and there- fore deposits from the Kerteminde Marl Formation (up to 100 m thick on Sjælland) are not found in the area, probably due to uplift during this time. Clastic marine sedimentation resumed during the up- per Selandian sea-level rise, and the North Sea, Denmark A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Æ Ø Å 20 μm 20 μm 20 μm 20 μm 20 μm 20 μm 20 μm 20 μm20 μm 20 μm 0.2 mm 0.5 mm 5 μm 5 μm 0.2 mm 0.2 mm 0.2 mm0.2 mm 0.2 mm 0.2 mm 5 μm 0.2 mm 10 μm 5 μm 5 μm5 μm 5 μm 0.2 mm 0.2 mm Fig. 3. Selected important nannofossils (A–H), microfossils (I–S) and dinocysts (T–Å). A: Discoaster kuepperi, B: Tribrachiatus orthostylus, C: Lophodolithus nascens, D: Neococcolithes protenus, E: Toweius occulatus, F: Imperiaster obscurus, G: Eiffellithus turriseiffelii, H: Prediscosphaera spi- nosa, I: Subbotina patagonica, J: Clavulina anglica, K: Gaudryina hilter- manni, L: Fenestrella antiqua, M: Coscinodiscus morsianus moelleri, N: Triceratium spp., O: Bolivina incrassata, P: Bolivinoides laevigatus, Q: Reusella szajnochae szajnochae, R: Stensioeina pommerana, S: Praebulimina levis, T: Eatonicysta furensis, U: Dracodinium? condylos, V: Ochetodinium romanum, W: Apectodinium hyperacanthum, X: Deflandrea oebisfeldensis, Y: Cerodinium medcalfii, Z: Isabelidinium? viborgense, Æ: Cannosphaerop- sis utinensis, Ø: Xenascus wetzelii, Å: Palaeoperidinium pyrophorum. 1616 and the German Basin formed a partly enclosed shelf area. The remainder of the Palaeogene (Æbelø, Holmehus, Ølst, Røsnæs Clay and Lillebælt Clay) formations mainly consist of fine-grained, plastic clay but there were many lithological shifts during this time. Deposition occurred in a relatively deep marine basin, although proximal to the shore. The changes in depositional conditions were related to changing circulation patterns in the North Sea and shifts in clay mineral provenance and periods of regression and non-deposition also occurred (Heilmann-Clausen et al. 1985). Intense volcanic ac- tivity caused by the opening of the North Atlantic resulted in ash deposition during the late Paleocene and Eocene. Quaternary glacial activity eroded, faulted and folded the Palaeogene sediments resulting in their present distribution (Fig. 4). The new biostratigraphic studies indicate that the Røsnæs Clay Formation is strongly folded with repeated stra- tigraphy, indicating movements along faults. The youngest formation in the area, the Lillebælt Clay Formation, occurs only as floes in the glacial sediments. On land, the Palaeo- gene clay seems to be undisturbed towards the north whereas disturbances increase towards the south. Conclusions The recent biostratigraphic study has provided important information about the pre-Quaternary deposits under the c. 18 km wide Femern Bælt, imperative to planning the con- struction of the Femern Bælt fixed link. The Cretaceous– Palaeogene Tor Formation equivalent, Danian limestone, Lellinge Greensand, Æbelø, Holmehus, Ølst, Røsnæs and Lillebælt Formations have been identified in multiple bore- holes using multidisciplinary biostratigraphy. This informa- tion, coupled with physical rock properties (Rambøll Arup JV 2011) allows a geological cross-section of the Femern Bælt to be established and demonstrates the complex nature of the depositional and structural history of the area. In addition, in situ Danian limestone has been discovered for the first time, along with Lellinge Greensand on Lolland in DGU core 241.213. The new data from >500 m fully cored boreholes provide an excellent basis for future detailed bio- stratigraphic, sedimentological and basin analysis of the Pal- aeogene deposits in the area. References Berggren, W.A., Kent, D.V., Swischer III, C.C. & Aubry, M.-P. 1995: A revised Cenozoic geochronology and chronostratigraphy. In: Berggren, W.A. et al. (eds): Geochronology, time scale and global stratigraphic correlation. Society for Sedimentary Geology (SEPM) Special Publica- tion 54, 129–212. Burnett, J.A. 1998: Upper Cretaceous. In: Bown, P.R. (ed.): Calcareous nan- nofossil biostratigraphy. British Micropalaeontological Society Series, 132–199. Clausen, O.R. & Huuse, M. 2002: Mid-Paleocene palaeogeograhpy of the Danish area. Bulletin of the Geologocal Society of Denmark 49, 171–186. 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Heilmann-Clausen, C. & Costa, L.I. 1989: Dinoflagellate Zonation of the Uppermost Paleocene? to lower Miocene in the Würsterheide Research Well, northwest Germany. Geologisches Jahrbuch A111, 431–521. Håkansson, E., & Pedersen, S.S. 1992: Kort over den danske undergrund. København: Varv (map sheet). Martini, E. 1971: Standard Tertiary and Quaternary calcareous nanno- plankton zonation. In: Farinacci, A. (ed.): Proceedings of the Second Planktonic Conference Roma. Edizioni Tecnoscienza, Rome 2, 739–785. Rambøll Arup JV 2011: Summary of geological conditions. Geotechnical Data Report 01.3-002, 53 pp. Virum: Femern A/S. Sheldon, E. & Nøhr-Hansen, H. 2010: Fehmarn Belt fixed link pre-Qua- ternary biostratigraphy – a final status report for Rambøll Arup Joint Venture. Danmarks og Grønlands Geologiske Undersøgelse Rapport 2010/134, 53 pp. Stouge, S., Hjortkjær, B.F., Rasmussen, J.A., Roncaglia, L. & Sheldon, E. 2000: Micro- and nannofossil biostratigraphy across the Danian/Selan- dian (Paleocene) stage boundary at Gemmas Allé, Copenhagen, Den- mark. GFF 122, 161–162. Stockholm: Geological Society of Sweden. Varol, O. 1998: Palaeogene. In: Bown, P.R. (ed.): Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Series, 200–224. Quaternary deposits Fehmarn 0 m 50 100 150 Lolland 3 km Folded and faulted Palaeogene clays Palaeogene formations Cretaceous Fig. 4. Simplified geological cross-section across the Femern Bælt. The fold- ing shown in the Palaeogene clay is for illustrative purposes only; the real nature of the disturbance (folding and faulting) is much more intense and complicated than shown (modified after Rambøll Arup JV 2011). Authors’ address Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. E-mail: es@geus.dk