NORWEGIAN JOURNAL OF GEOLOGY Vol 99 Nr. 4 https://dx.doi.org/10.17850/njg99-4-1 Correlation of the Upper Oligocene–Miocene deltaic to shelfal succession onshore Denmark with similar deposits in the northern North Sea and Norwegian Sea shelf based on Sr isotope-, bio- and seismic stratigraphy—a review Tor Eidvin1, Erik Skovbjerg Rasmussen2, Fridtjof Riis1, Karen Dybkjær2 & Kari Grøsfjeld3 1Norwegian Petroleum Directorate (NPD), Professor Olav Hanssens vei 10, P. O. Box 600, NO–4003 Stavanger, Norway. 2Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, DK–1350, Copenhagen K, Denmark. 3Geological Survey of Norway, Leif Eirikssons vei 39, P. O. Box 6315 Torgarden, NO–7491 Trondheim, Norway E-mail corresponding author (Tor Eidvin): [email protected] The almost complete, mainly deltaic, upper Paleogene and Neogene succession in Jylland, Denmark, was previously investigated for 87Sr/86Sr ratios in 143 samples from 18 localities. In the present paper, strontium-isotope data from the Upper Oligocene–Lower Miocene parts and foraminiferal and pyritised diatoms data from 94 of these samples were used to correlate with previously published data from Norwegian wells and boreholes and one borehole in the British sector of the North Sea. For the Middle–Upper Miocene parts of the succession the correlation is based mainly on Bolboforma data. The ages of the geological formations in the Danish succession correlate readily with lithological units in the Norwegian North Sea, the Norwegian Sea shelf and the East Shetland Platform, which have all been investigated applying similar methods. The Bolboforma assemblages have their origin in the North Atlantic and the Norwegian Sea and confirm the presence of an open strait in the northern North Sea. This strait was the only seaway passage into the North Sea Basin during the Miocene. The glauconitic Utsira Formation sand (approximately 5.7–4.2 Ma), in the threshold area close to the outlet to the Norwegian Sea, overlies erosional unconformities comprising hiati of 21 my in some areas and 13 my in other areas. We believe that the unconformity below the Utsira Formation was mainly related to a fall in sea level in the Late Miocene, contemporaneous with that partly responsible for the Messinian salinity crisis. Bolboforma and dinoflagellate cysts stratigraphy indicate that the base of the Molo Formation in its southern distribution area (Draugen Field, Trøndelag Platform) is of Late Miocene age (close to 9 Ma). This part of the Molo Formation was contemporaneous with the middle/upper part of the Kai Formation. Keywords: Sr isotope stratigraphy, foraminiferal stratigraphy, Bolboforma stratigraphy, upper Paleogene-Neogene correlation, Denmark, North Sea, Norwegian Sea shelf, Norwegian Sea. Received 30. May 2019 / Accepted 25. September 2019 / Published online 30. October 2019 Introduction understanding the palaeogeography and infill history of the North Sea basin. A proper dating of the sedimentary A correlation between the well-dated outcropping Upper units and recognition of the extent of hiatuses are Oligocene–Miocene succession in Denmark (Eidvin et necessary for this purpose. al., 2014a) and the offshore succession in the Norwegian North Sea, East Shetland Platform and Norwegian Sea Thin-walled calcareous microfossils such as foraminifera shelf (Eidvin, 2016; Eidvin et al., 2013, 2014b) is a key for and Bolboforma are generally sparse in the Danish Eidvin, T., Rasmussen, E.S., Riis, F., Dybkjær, K. & Grøsfjeld, K. 2019: Correlation of the Upper Oligocene–Miocene deltaic to shelfal succession onshore Denmark with similar deposits in the northern North Sea and Norwegian Sea shelf based on Sr isotope-, bio- and seismic stratigraphy – a review. Norwegian Journal of Geology 99, 543–573. https://dx.doi.org/10.17850/njg99-4-1. © Copyright the authors. This work is licensed under a Creative Commons Attribution 4.0 International License. 543 544 T. Eidvin et al. onshore upper Paleogene and Neogene successions. This Eidvin et al. (2014a) presented a comparison and is either due to their dissolution by humic acid in the a discussion of the Danish strontium-isotope and pore water or they were not present in the most marginal dinocyst data. They concluded that the Sr isotope ages marine environments. However, from the stratigraphic from the lower part of the Danish Miocene succession, borehole Rødding (DGU nr. 141.1141) in southern i.e., the latest Oligocene–Early Miocene Brejning to Jylland (Fig. 1), Eidvin et al. (2013) were able to retrieve Odderup formations, agree with the age estimates based foraminifera, Bolboforma and mollusc shells from most on dinocysts. However, the 87Sr/86Sr ratios of fossil sections (Figs. 1 & 2). In several sites, investigated for carbonates from the Middle–Upper Miocene, Hodde fossil dinoflagellate cysts (dinocysts) by Dybkjær & to Gram formations consistently indicate ages older Piasecki (2010), thick-walled tests of molluscs have than those recorded by the dinocysts (Fig. 2). Post- been quite resistant to dissolution. These are present depositional processes as an explanation for this offset where foraminifera are absent, and Eidvin et al. (2014a) are inconsistent with the good preservation of the shell succeeded to retrieve molluscs and/or mollusc fragments material. There is also restricted reworking. Eidvin et al. from a number of samples for strontium isotope analyses (2014a) suggested that limited oceanic exchange with the from these sites (Table 1). inner North Sea Basin might have caused the observed Sr isotope ratios. Boreholes/wells 100 km Exposures Frida-1 Studied localities Lone-1 North Sea Jylland 50 km S-1 Tove-1 57°N Limfjorden Sweden Salling Lyby Strand Harre-1 Denmark Præstbjerg Fasterholt Jylland 55°N Sdr. Vium Jensgård Fakkegrav Dykær Vejle Fjord Føvling Brejning Bøgeskov Sjælland Gram-2 Rødding Fyn Gram 53°N Lille Tønde Hørup Hav Klintinghoved Germany 8°E 10°E 12°E Figure 1. Map of onshore and offshore Denmark showing wells, boreholes and outcrops analysed for dinocysts (Dybkjær & Piasecki, 2010), Bolboforma and foraminifera (Eidvin et al. 2013). It also shows the sites where shell material has been Sr dated. Small circles: Outcrops and boreholes which formed the basis for the dinocyst study (Dybkjær & Piasecki, 2010). Large circles: Outcrops and boreholes that formed the basis for the dinocystFig. study 1 (Dybkjær & Piasecki, 2010) as well as the present Sr isotope study. NORWEGIAN JOURNAL OF GEOLOGY Correlation of the Upper Oligocene–Miocene deltaic to shelfal succession onshore Denmark with similar deposits Table 1. Strontium-isotope analyses (all samples are analysed at the University in Bergen if not stated otherwise. All Sr ratios were corrected to NIST 987 = 0.710248. Numerical ages derived from the SIS Look-up Tables of Howarth & McArthur (1997, 2004). NIST – National Institute for Standard and Technology. DC – ditch cuttings). Corrected Age (Ma; H. & M., 1997; Age (Ma; H. & M., 2004; Localities Lithostratigraphy/sample level 2S error Comments Analysed fossils 87/86Sr mean value) mean value) Brejning (outcrop) Brejning Fm 0.708202 0.000009 24.84 23.99 One mollusc fragment Brejning (outcrop) Brejning Fm 0.708193 0.000008 24.98 24.16 Same sample as above One mollusc fragment Dykær (outcrop) Brejning Fm 0.708272 0.000008 23.74 22.68 Two mollusc fragments Dykær (outcrop) Brejning Fm 0.708273 0.000008 23.72 22.67 Same sample as above Two mollusc fragments Fakkegrav (outcrop) Brejning Fm 0.708163 0.000009 25.53 24.78 One mollusc fragment Fakkegrav (outcrop) Brejning Fm 0.708161 0.000008 25.57 24.83 Same sample as above One mollusc fragment Bøgeskov (outcrop) Brejning Fm 0.708287 0.000008 23.46 22.43 One mollusc fragment Bøgeskov (outcrop) Brejning Fm 0.708275 0.000008 23.69 22.63 Same sample as above One mollusc fragment Jensgård (outcrop) Brejning Fm 0.708164 0.000008 25.51 24.76 One mollusc fragment Jensgård (outcrop) Brejning Fm 0.708155 0.000008 25.68 24.99 Same sample as above One mollusc fragment Lyby Strand (outcrop) Brejning Fm 0.708202 0.000008 24.84 23.99 One mollusc fragment Lyby Strand (outcrop) Brejning Fm 0.708231 0.000008 24.42 23.93 Same sample as above One mollusc fragment Hørup Hav (boreh.) Brejning Fm? 76.8–76.4 m (bucket) 0.708243 0.000009 24.23 23.20 One mollusc fragment Harre (borehole, core) Brejning Fm, 44.25 m (core) 0.708174 0.000008 25.32 24.53 Two mollusc fragments Harre (boreh.) Brejning Fm, 44.25 m (core) 0.708212 0.000008 24.70 23.81 Three mollusc fragments Harre (boreh.) Brejning Fm, 37.25 m (core) 0.708202 0.000008 24.84 23.99 One mollusc fragment Harre (boreh.) Brejning Fm, 31.25 m (core) 0.708190 0.000009 25.03 24.22 One mollusc fragment Rødding (boreh.) Vejle Fjord Fm, 243 m (DC) 0.708265 0.000009 23.86 22.80 One mollusc fragment Rødding (boreh.) Vejle Fjord Fm, 241 m (DC) 0.708199 0.000009 24.89 24.05 One mollusc fragment Salling 1 (outcrop) Vejle Fjord Fm 0.708313 0.000009 22.88 22.06 Three mollusc fragments Salling 1 (outcrop) Vejle Fjord Fm 0.708297 0.000008 23.25 22.28 Six mollusc fragments Salling 1 (outcrop) Vejle Fjord Fm 0.708318 0.000008 22.76 21.99 Same sample as the two above One mollusc fragment Fasterholt (boreh.) Vejle Fjord Fm, 170 m (core) 0.708259 0.000009 23.97 22.91 One mollusc fragment Fasterholt (boreh.) Vejle Fjord Fm, 170 m (core) 0.708266 0.000008 23.85 22.79 One mollusc fragment Fasterholt (boreh.) Vejle Fjord Fm, 170 m (core) 0.708284 0.000008 23.52 22.48 One mollusc fragment Hørup Hav (boreh.) Vejle Fjord Fm, 68.8–68.4 m (bucket) 0.708302 0.000009 23.14 22.22 One mollusc fragment Harre (boreh.) Vejle Fjord Fm, 19.75 m (core) 0.708252 0.000009 24.08 23.03 One mollusc fragment Rødding (boreh.) Vejle Fjord Fm, 238 m (DC) 0.708233 0.000008 24.54 23.39 One mollusc fragment Rødding (boreh.) Vejle Fjord Fm, 236 m (DC) 0.708258 0.000008 23.99 22.93 Three mollusc fragments 545 Rødding (boreh.) Vejle Fjord Fm, 230 m 0.708232 0.000009 24.41 23.41 One mollusc fragment Continues T.