Abstract. The lower Oligocene (Rupelian) successions are climate
record archives of the early icehouse world in the Cenozoic. Even though the number of studies focussing on the generally cold Oligocene is increasing,
little is known about climatic variations in the mid-latitudes to high latitudes of
the Northern Hemisphere. One of the major obstacles is the lack of
stratigraphically complete uppermost Eocene to Oligocene successions in
these regions. This study focusses on dinoflagellate cysts (dinocysts) from a
thick nearly complete Rupelian succession in the Syracuse Oils Norge A/S
well 11/10-1 drilled in 1969 in the Norwegian part of the North Sea basin.
The well provides a record of mid-latitude dinocyst assemblages, which yield
key biostratigraphical and palaeoenvironmental information. All the analyses were undertaken on ditch cutting samples. The dinocyst
assemblages confirm that the well penetrates about 600 m of Rupelian
sediments and (as supported by correlation with the Nini-1 well) that the
lowermost Rupelian (below the top or the last occurrence of Areosphaeridium diktyoplokum) is expanded.
These assemblages also indicate the presence of two hiatuses: the first extends
from the Lutetian to the Priabonian (equivalent to the D9nb–D12nb zones), and
the second spans the Rupelian–Chattian boundary (equivalent to the D14nb
subzone or the NSO-5 zone). Despite the risk of caving, the dinocyst
assemblages support the existing sequence stratigraphic framework. The
assemblages reflect a clear transition from distal to proximal deposition in
the vicinity of the site (across the regional seismic sequences OSS-1 – OSS meaning Oligocene seismic sequence – to
OSS-2). The proximal deltaic deposits of the OSS-2 regressive system tract (RST) are characterised by
pulses of high sea-surface productivity and pronounced shifts in the
dinocyst assemblages, reflecting a highly dynamic environment in a
restricted marine to marginal marine setting. The Rupelian succession penetrated by well 11/10-1 yields one new species,
Areoligera? barskii sp. nov., which is described here in detail. The cold-water-tolerant dinocyst Svalbardella cooksoniae is present in two intervals in the studied
succession. These intervals are related to the early Oligocene cooling
maxima (the Oi-1a and the Oi-2 events). Furthermore, these two intervals
correlate with two local sequence boundaries, suggesting that they are most
probably of glacioeustatic origin. From these observations, I postulate that
the early icehouse climate played an important role in the depositional
development of the Oligocene succession in the North Sea basin. Even though
the Eocene–Oligocene transition interval is not complete (i.e. Lutetian to
Priabonian is either missing or condensed), well 11/10-1 merits
high-resolution studies of the early icehouse climate for the North Sea
region. Although any detailed studies should ideally be undertaken on
conventional cores instead of ditch cuttings, no such samples spanning the
Eocene–Oligocene transition exist in this area.
A fossil albatross from the Early Oligocene of the North Sea Basin
