Neogene dinocyst zonation for the eastern North Sea Basin, Denmark

A dinocyst zonation for the Neogene succession in the eastern part of the North Sea Basin (Denmark) is presented. The zonation is based on an extensive database comprising data from more than fifty onshore and offshore boreholes and about twenty five outcrops. Most of the nineteen dinocyst zones described and defined herein, are new. The zonation is correlated with previously published dinocyst zonations within the North Sea Basin, in the North Atlantic and with the revised Northwest European zonation. The presented zonation gives a detailed subdivision of the Oligocene–Miocene transition, of the Lower Miocene, and of the Upper Miocene and Pliocene successions. The previous zonation of the onshore Danish Middle Miocene is reconsidered and partly redefined.The zonation is correlated with other biostratigraphic subdivisions of the Neogene succession in the Danish region in addition to litho- and sequence stratigraphy. The dinocyst zonation and the foraminifer zonation of the Danish Miocene (based upon analysis of the same boreholes) were independently calibrated with the established nannoplankton zonation. This correlation revealed a mismatch generally corresponding to one nannoplankton zone.Absolute ages of the new dinocyst zones are proposed based on correlation from the studied succession within the North Sea Basin with the international zonations and stratigraphic schemes. In addition, parts of the succession have been dated by strontium isotope analysis of mollusc shells. Inconsistencies due to first and last occurrences of some dinocyst species in previous studies and the present study, especially within the Lower Miocene, implied that new Sr-isotope datings from mollusc shells from the cored Sdr. Vium borehole and other localities in this study would be invaluable. Indeed, this method allowed the previous last occurrence of Cordosphaeridium cantharellus (one of the zonal index fossils) dated as between 17.95 My and 19.5 My in previous studies, to be assigned a new dating of 18.4 My. The timespan of the zones range from 2.6 My for the Amiculospharea umbraculum Zone to 0.4 My for the Achomosphaera andalousiensis Zone.Neogene biostratigraphy in the North Sea Basin has been problematic due to the periodically limited connection between the North Sea Basin and the North Atlantic Ocean, especially with respect to stratigraphy based on foraminifers and calcareous nannoplankton. Many of the stratigraphically most important taxa, e.g. those defining stratigraphic boundaries in type sections, have not been found within the North Sea Basin. This problem seems to be solved by correlation based on the new dinocyst stratigraphy, because stratigraphically significant taxa do occur in the North Sea deposits, even in marginal marine settings.