MIDDLE EOCENE TO LATE OLIGOCENE GLACIO-EUSTATIC DRIVEN UNCONFORMITIES FROM THE SOUTHERN NORTH SEA BASIN: APPLIED PALEOCLIMATOLOGY IN UNDERSTANDING THE HISTORICAL UNIT-STRATOTYPES

The Eocene and Oligocene Epochs represent critical phases in earth history, reflected in major climatic and oceanographic changes. Detailed records of deep-water temperature show a gradual climatic cooling, with superimposed strong short-term fluctuations. Data from continental shelf areas however are scarce, hampering assessment of possible coupling of responses between oceanic and epicontinental domains. Since the greater North Sea is one of the best-documented passive margin systems, which accommodates several internationally selected Paleogene Stages, it is a key area for unravelling the Paleogene depositional history, including the positioning and dating of unconformities and for monitoring paleowatertemperature evolution. The latter is based on quantitative micropaleontology, allowing determining relative paleotemperature trends (Van Simaeys et al., 2004, 2005; De Man et al., 2004) and on otolith and benthic foraminifer oxygen isotope evidence, revealing seasonal variations and mean annual temperature trends.

Similar to the New Jersey sequences (e.g., Pekar et al., 2002), several Eocene and Oligocene sequence boundaries from the North Sea Basin show good correlation with global, deep-sea benthic foraminiferal oxygen isotope maximums, suggesting a glacio-eustatic control. Exemplary for this model are the Priabonian/Rupelian (P/R) and Rupelian/Chattian (R/C) transitions. The former is identified by means of dinocysts (Vandenberghe et al., 2003) and is positioned well below the major shift in mean annual temperatures which co-occurs with a dramatic faunistic reorganisation. The R/C transition coincides with major changes in paleotemperature and paleobathymetry. The abundance of the arctic dinocyst taxon Svalbardella, correlating with the R/C unconformity and the Oi2b-event (Miller et al., 1998) implies a major mid-Oligocene glaciation (Van Simaeys et al., 2005); whereas the presence of subtropical benthic foraminifera at the base of the Chattian unit-stratotype are indicative for a worldwide sea level rise as a response to the ‘Late Oligocene Warming Event' (De Man & Van Simaeys, 2004). Attributing the Oi2b-event to the R/C unconformity in the southern North Sea Basin would involve an age for the base of the Chattian unit-stratotype not older than 27 Ma.