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

Abstract

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.