A mid-Oligocene cooling (Oi-2b) reflected in the dinoflagellate record and in depositional sequence architecture. An integrated study from the eastern North Sea Basin

Integrated micropaleontological (dinoflagellate and foraminifera) and 3D seismic studies of Oligocene surfaces were carried out in the eastern North Sea in order to investigate the influence of the climate on the evolution of depositional geometries and surface morphologies.Age-indicative dinoflagellates allowed a correlation of the succession with the global time scale and thereby with published oxygen isotope curves. Temperature-indicative dinoflagellate taxa furthermore allowed to infer paleoclimatic changes during the mid-Oligocene.One of the surfaces studied on 3D seismic datasets shows features such as low-angle landward directed onlaps, incised valleys and pockmarks, indicating a prominent, relative sea-level fall. The cold-water dinoflagellate Svalbardella was recorded immediately above this surface. The coincidence of a cold-water indicator with this distinctive sequence boundary shows that deposition of this sequence was controlled by climatically induced sea-level changes, and that 3D seismic analysis combined with high-resolution dinoflagellate analysis substantially improves the understanding of the depositional history and processes within the North Sea Basin. The Svalbardella event represents the Oi-2b glaciation and coincides with the onshore NW European Rupelian/Chattian boundary.