For the first time a dinoflagellate cyst zonation for the complete Neogene succession in the North Sea Basin has been defined.

In large areas of onshore Jylland, in western Denmark, sand bodies within the uppermost Oligocene – Miocene succession serve as important aquifers. The Neogene succession is unconformably overlain by Pleistocene deposits, but outcrops in inland pits and several coastal cliffs. The succession comprises three large deltasystems interfingering with marine mud. As the deltaic sand bodies cannot be discriminated upon lithological criteria, dinoflagellate cyst stratigraphy played an important role in mapping these aquifers. A strict biostratigraphic framework has been set up based on analyses of dinoflagellate floras in more than 60 boreholes throughout the region, combined with studies of 28 outcrops. A series of stratigraphic events (first appearances, last occurrences and acmes of dinoflagellate cyst species) occurring in most of the studied wells have been used for correlation of both mud and sand bodies. Parts of the Miocene succession comprise proximal deposits dominated by terrestrial palynomorphs. However, consistent occurrence of dinoflagellate cysts also in these environments, provides the most rigid tool for dating and correlation of these deposits. The fully marine parts of the succession provide excellent dinoflagellate cyst floras which correlate with contemporaneous North Atlantic floras. Lateral variations in the dinoflagellate cyst assemblages are ascribed to proximal-distal changes in the depositional environment.

                      These data, combined with data from a few North Sea offshore wells with more expanded and stratigraphically more complete successions, have resulted in a new dinoflagellate cyst zonation for the Neogene in Denmark. A total of 19 zones have been defined, the four uppermost zones are not recorded in the onshore succession, where the uppermost Miocene (Messinian) and Pliocene are absent. The new zonation thus provides a much more detailed stratigraphic resolution and a better dating of the Danish Neogene than the previous microfossil zonations (foraminifera- and nannofossil zonations).

References

Dybkjær, K. and Piasecki, S. (2010). Neogene dinocyst zonation in the eastern North Sea Basin, Denmark. Review of Palaeobotany and Palynology, 161, 1-29.