Deep-water agglutinated foraminifers (DWAF) have been used in biostratigraphic correlation in the North Sea and Norwegian Sea since the 1970s. The first round of deep-sea drilling (Leg 38) revealed that the Paleogene sediments recovered from the Norwegian Sea contain a fairly continuous record of microfossil assemblages composed almost exclusively of DWAF (Talwani, Udintsev et al., 1976). In nearly all the Deep Sea Drilling Project (DSDP)/Ocean Drilling Program (ODP) holes from the Norwegian Sea region, Paleogene calcareous benthic foraminifers are either completely lacking or have been found only in discrete horizons at comparatively shallow sites on the Vøring Plateau (Hulsbos et al., 1989). In their synthesis of the Paleogene material from Leg 38 sites, Verdenius and van Hinte (1983) succeeded in subdividing the Paleogene record into a number of assemblage zones that were useful for local stratigraphic correlation.
During the early 1980s, several biostratigraphic schemes based on agglutinated foraminifers were devised for the Paleogene of the North Sea region (Gradstein and Berggren, 1981; King, 1983; Gradstein et al., 1988). It became apparent that a number of Eocene-Oligocene DWAF species occur throughout the North Sea, Norwegian Sea, and Labrador Sea, suggesting that they may be useful for correlation purposes throughout the northern part of the North Atlantic. Subsequent studies have further refined the taxonomy and biostratigraphy of Norwegian Sea DWAF (Gradstein and Kaminski, 1989; Kaminski et al., 1990; Osterman and Spiegler, 1996; Kaminski and Geroch, 1997; Nagy et al., in press; Gradstein and Kaminski, 1997). Quantitative studies of biostratigraphic data from 33 North Sea and Norwegian Sea exploration wells have yielded a refined biostratigraphic zonation of the area using DWAF and other microfossils (Gradstein et al., 1988; Gradstein et al., 1992, 1994; Gradstein and Bäckström, 1996).
Initial shipboard investigations revealed that a thick sequence of Oligocene sediments containing rich DWAF assemblages, but few other microfossil remains, was recovered from Hole 985A. Our primary purpose in studying this material was to refine the biostratigraphy of the Oligocene/Miocene transition in the Norwegian Sea at a site that appears to contain a much-expanded Oligocene section. Because of its location in the central part of the Norwegian Sea, we expected Hole 985A to contain a more continuous Oligocene record than at Site 643 on the Vøring Slope or elsewhere on the Vøring Plateau, an area where sedimentation may have been influenced by oceanic currents. The Oligocene at Site 643 is considerably thinner than at Site 985, and one or more hiatuses may be present at Site 643 (Kaminski et al., 1990). Additionally, our second purpose for studying the DWAF was to undertake detailed observations of the morphology and wall structure of selected species that were first described from the North Sea region (M.A. Kaminski and W.E.N. Austin, unpubl. data). Because of the thick overburden in the North Sea region, Oligocene forms are typically silicified and compressed. At Site 985, on the other hand, the Neogene sediments are relatively thin; as a result, the DWAF display excellent preservation.
At present the chronostratigraphic control at Site 985 remains poor because of the lack of calcareous microfossils that would enable correlation with the standard planktonic zonal schemes. The sequence was dated by means of magnetic polarity records to the latest Miocene; below this, it was difficult to correlate with the geomagnetic polarity time scale (Shipboard Scientific Party, 1996). Thus, the underlying sequence has poor age constraints. We hope that future palynological studies from this hole may enable a better correlation with the standard zonal schemes. The poor independent age control means that chronostratigraphic assignments are based solely on agglutinated foraminifers. We achieved this by correlating our biostratigraphic sequence with the Oligocene benthic foraminiferal zonations developed for the Norwegian and North Sea regions.