Stratigraphic distribution charts for the dinoflagellate cysts recovered from Holes 986C and 986D are presented in Appendix A and Appendix B (on oversize figure, this volume). Dinoflagellate cysts are recovered from all 82 examined samples. Preservation is generally good, but abundance and species diversity vary significantly throughout the studied Pliocene-Pleistocene succession. More than 290 different taxa of dinoflagellate cysts have been identified from Hole 986C (38 samples), and 208 different taxa have been recovered from Hole 986D (44 samples). A number of species have been identified only to genus level, and several species are listed under open nomenclature in the range charts. As pointed out by Mudie (1989), many species found in the Neogene of the Norwegian-Greenland Sea are still not formally described. To some extent, this hampers the potential use of Neogene dinoflagellate cysts for biostratigraphy and regional correlations. One important observation from this site, however, is that most of the taxa recovered from Holes 986C and 986D are not in situ but reworked Mesozoic and Paleogene dinoflagellates. Although the diversity of in situ taxa seems to decline upward into the Pleistocene, the total diversity of recovered species shows a more erratic picture. Periods with extensive reworking on the Barents Shelf and Svalbard can apparently be related to periods with extensive erosion and reworking following the change to glacially dominated depositional regimes in the late Pliocene-Pleistocene.
The lower boundary of this seismic unit corresponds to the basement estimated at 1170 mbsf; the top corresponds to seismic Reflector R7 (Fig. 2). This onlaps an elevated block of the oceanic basement east of the Knipovich Ridge (Myhre and Eldholm, 1988). Estimates of the spreading rate suggest that the ridge block is not older than 5-6 Ma (Sundvor and Eldholm, 1979; Hjelstuen et al., 1996). Farther south in the Lofoten Basin, the termination of Reflector R7 onto oceanic basement indicates that this seismic boundary is not older than 5.2 Ma (Fiedler, 1992).
Hole 986D was terminated at 964.6 mbsf, whereas the lowest palynological sample is from 955.74 mbsf. The age of this lowest sample is difficult to date. The marker species having their last appearance datums (LADs) at the top of Zone Mio6 of Poulsen et al. (1996) have not been found in Unit SV-VIII, indicating that this unit is not as old as the NN 11 Zone. The presence of Sumatradinium pliocenicum Head 1993 throughout this unit further supports an age not older than early Pliocene, but the total range of this species is presently not well documented (Head, 1993). Filisphaera filifera, which Mudie (1989) used as a marker for her Filisphaera filifera-PM2 Zone, has its lowest occurrence at 909.14 mbsf. The base of the PM2 Zone was calibrated to ~4.2 Ma based on magnetostratigraphic data. More recent observations, however, suggest that F. filifera also ranges into the upper (and mid?) Miocene (Poulsen et al., 1996).
Reticulatosphaera actinocoronata is common from the lowest investigated samples at 955.74 m up to 909.14 mbsf, where the species has its last in situ occurrence. Poulsen et al. (1996) used the last occurrence of this species to define the top of their Pli1 Zone of early Pliocene age (dated as equivalent to the NN 12-14 Zones). In contrast, Mudie and Harland (1996) placed the LAD of R. actinocoronata at the top of the Olduvai magnetostratigraphic Subchron, suggesting a significantly younger age for this dinoflagellate LAD. Further, according to Mudie and Harland (1996), Invertocysta lacrymosa also has its LAD at the top of the Olduvai Subchron. In Hole 986D, this species has its highest occurrence at 909.14 mbsf. An age as young as late Pliocene (~1.65 Ma) at this level is, however, not supported by foraminifer biostratigraphy (Eidvin and Nagy, Chap. 1, this volume), magnetostratigraphy, and seismic correlations (Channell et al., Chap. 10, this volume). It should be noted that Poulsen et al. (1996) used the LAD of Invertocysta lacrymosa to define the top of their Pli3 Zone of late Pliocene age (equivalent to NN 16-18 Zones). In a recent study on the impact of the onset of major Northern Hemisphere glaciations on the dinoflagellate cyst assemblages in the Mediterranean and the North Atlantic (Site 607), Versteegh (1997) found that the LAD of Invertocysta lacrymosa appears to be a valuable marker for oxygen isotope Stage 110. If this is valid for Hole 986, then a late Pliocene age of ~2.74 Ma is suggested at 909.14 mbsf.
The LAD of Selenopemphix brevispinosa at 928.34 mbsf may prove to be a more reliable marker within Unit SV-VIII. According to Head (pers. comm., 1991), this species has its LAD within the early late Pliocene (e.g., beds correlatable to the NN 16 Zone). This event supports an age of ~2.6-2.7 Ma for the lowermost part Hole 986D.
The lower boundary of this unit corresponds to seismic Reflector R7. This reflector marks the onset of the major glacial sedimentation along the Svalbard-Barents Shelf margin. Based on the foraminifer biostratigraphy in wells on the Senja Ridge (Eidvin et al., 1993) and dating by Ar isotopes from a shallow borehole in the Bjørnøya West area (Mørk and Duncan, 1993), an age of ~2.3 Ma has been assigned to this reflector (Faleide et al., 1996). Paleomagnetic data suggest that the top of the Olduvai Chron can be placed at 735 mbsf in this zone, whereas the base of the Olduvai is found at 756 mbsf (Channell et al., Chap. 10, this volume) and hence have ages of ~1.77 and 1.95 Ma, respectively. The upper boundary of this unit corresponds to seismic Reflector R6 (Fig. 2, Fig. 3).
There are very few age-diagnostic dinoflagellate events recognized in this unit. In their study of the Pliocene-Pleistocene sequences during Leg 151, Hole 911A, on the Yermak Plateau, Matthiessen and Brenner (1996) noted a distinct abundance peak of Filisphaera filifera in the upper Pliocene. In Hole 986D, a small acme of this species is recognized at 804.84 mbsf. Selenopemphix dioneaecysta is also present up to 849.94 mbsf; to our knowledge, this species is not reported from post-Pliocene strata.
Sumatradinium pliocenicum is common and consistently present up to 564.44 mbsf, where it has its last occurrence. This species was originally described from the upper Pliocene of southwestern England and is not known to range above the Pliocene (Head, 1993). An age not younger than 1.65 Ma is thus suggested for the uppermost part of seismic Unit SV-VII.
The lower boundary of this unit corresponds to seismic Reflector R6. The upper boundary is defined by Reflector R5 (Fig. 2, Fig. 3).
The age of this unit is difficult to interpret based on dinoflagellate cysts alone. The lower part of the unit is characterized by common to abundant Brigantedinium spp. and Bitectatodinium tepikiense. The LAD of Tectatodinium pellitum is noted at 516.44 mbsf. Poulsen et al. (1996) use the LAD of this species, together with the LADs of Amiculosphaera umbracula, Filisphaera filifera, Impagidinium japonicum, I. multiplexum, and I. velorum, to define the top of their Qty1 Zone (correlated to the NN 18 and 19 nannoplankton zones). A. umbracula is recognized in the lower part of Unit SV-VI but has its LAD in the overlying unit SV-VB (at 333.53 mbsf). Based on this, a general early Pleistocene age is suggested for this unit.
The lower boundary of this unit corresponds to seismic Reflector R5. This reflector is recognized as an important seismic sequence boundary along the entire Svalbard-Barents Shelf margin (Faleide et al., 1996). Based on correlations with increased amounts of ice-rafted detritus and oxygen-isotope measurements elsewhere in the Norwegian-Greenland Sea, Faleide et al. (1996) assigned a likely age of 1.0 Ma to Reflector R5. The upper boundary of this unit is defined by seismic Reflector R4A (Fig. 2, Fig. 3).
The marine microfloras found in Unit SV-VB are broadly comparable to those of the underlying unit, although there appears to be a relative decline in the abundance of Operculodinium centrocarpum and Spiniferites spp. Age determinations based on dinoflagellate cysts are problematic, although the uppermost occurrence of Amiculosphaera umbracula at 333.53 mbsf may be taken as evidence of an early Pleistocene age at this level. Mudie and Harland (1996) questionably placed the LAD of this species at ~1.5 Ma. Poulsen et al. (1996) used, among others, the LAD of A. umbracula to define the top of their Qty1 zone, which they correlated with the top of the NN 19 Zone. An early Pleistocene age is therefore likely for Unit SV-VB.
The lower boundary of this unit is defined by seismic Reflector R4A, whereas the upper boundary corresponds to Reflector R4 (Fig. 2, Fig. 3). Following the decline in numbers of dinoflagellate cysts at the top of the underlying unit, Unit SV-VA is characterized by relatively increased abundances of Operculodinium centrocarpum, Spiniferites spp., and Bitectatodinium tepikiense. The lowest occurrence of Spiniferites elongatus is observed at 235.44 mbsf. An acme of Achomosphaera andalousiensis is noted at 200.04 m.
An early Pleistocene age is assigned based on the unit's stratigraphic position above Reflector R5 and by the presence of Operculodinium israelianum throughout the unit. These factors suggest an early Pleistocene age, which is supported by measurements from the wireline logs indicating that the Cobb Mountain Event of 1.2 Ma can be recognized at around 200 mbsf.
The lower boundary of this unit is defined by seismic Reflector R4; the upper boundary, by Reflector R3 (Fig. 2, Fig. 3). Channell et al. (Chap. 10, this volume) identified the top Jaramillo Event at 148 mbsf, giving an age of 0.99 Ma at this level. The Brunhes/Matuyama paleomagnetic boundary seems to be located at ~127 mbsf in this unit (Channell et al., Chap. 10, this volume). This event points to an age of 0.78 Ma at this stratigraphic level.
The dinoflagellate assemblages from this unit are, in overall character, comparable to those of the underlying unit. However, a marked decrease in the relative abundances of Bitectatodinium tepikiense and Operculodinium centrocarpum occur in the upper part of the unit. The presence of Operculodinium israelianum through this unit suggests a continuing assignment to the early Pleistocene.
The lower boundary of this unit is defined by seismic Reflector R3; the upper boundary corresponds to Reflector R2 (Fig. 2, Fig. 3). A mid-Pleistocene age of 0.46 Ma has previously been assigned to this unit based on the last occurrence of Pseudomiliania lacunosa at 125.83 mbsf (Jansen, Raymo, Blum, et al., 1996).
This unit differs from the underlying early Pleistocene units by containing lower abundances of the dinoflagellates Bitectatodinium tepikiense and Operculodinium centrocarpum. The relative proportion of Brigantedinium spp. appears comparable to those of the underlying Pleistocene units. Spiniferites elongatus is present throughout the unit. The LAD of Operculodinium israelianum at 122.18 mbsf indicate that the early/mid-Pleistocene boundary is close to this level. Harland (1992) and Mudie and Harland (1996) suggested that this species disappeared in the mid-Pleistocene in the North Atlantic region. This LAD gives an age of ~0.73 Ma at 122.18 mbsf, somewhat older than that suggested by the foraminifers.
The lower boundary of Unit SV-II is defined by seismic Reflector R2; the upper boundary, by Reflector R1 (Fig. 2, Fig. 3).
An acme of Operculodinium centrocarpum and a minor abundance peak of Spiniferites spp. (including S. elongatus) are found in the lower part of the unit (66.04 mbsf). The abundance peak of O. centrocarpum is recorded between 66.04 and 58.04 mbsf. This may correlate with a comparable acme at 98.95 mbsf at Hole 911A on the Yermak Plateau. This event has been dated as 0.5 Ma (Matthiessen and Brenner, 1996).
Otherwise, Unit SV-II is characterized by low abundances of in situ dinoflagellate cysts. The LAD (a minor abundance peak) of Filisphaera filifera is also recognized at 66.04 mbsf. According to Mudie and Harland (1996), the LAD of this species is found near the base of the middle Pleistocene. An age as old as the base of the Brunhes magnetochron at 66.04 m, however, does not agree with the age determinations made for the underlying Unit SV-III.
Matthiessen and Brenner (1996) observed a distinct drop in the relative abundance of Brigantedinium spp. and an associated increase in the abundance of Operculodinium centrocarpum between 33.73 and 43.21 mbsf in Hole 911A on the Yermak Plateau. This turnover in assemblage was dated at ~0.5 Ma. A comparable change is observed at the transition between Units SV-III and SV-II in Hole 986C.
The lower boundary of Unit SV-I is defined by seismic Reflector R1 (Fig. 2, Fig. 3). The sediments above this reflector all belong to the Brunhes normal polarity epoch and must therefore be younger than 0.73 Ma (Channell et al., Chap. 10, this volume). Amino-acid analyses further indicate an age younger than 0.44 Ma (Faleide et al., 1996).
In situ dinoflagellate cysts are sparse in this unit but include characteristic taxa such as Achomosphaera andalousiensis, Algidasphaeridium? minutum, Bitectatodinium tepikiense, Brigantedinium spp., Spiniferites elongatus, Operculodinium centrocarpum, and Nematosphaeropsis labyrinthea. Most are taxa occurring in the western North Atlantic today. No exclusive Holocene taxa (like Protoperidinium oblongum) have been recovered, but the marked increase in the relative abundance of O. centrocarpum and Spiniferites spp. in the uppermost part of the unit (11.24-3.74 mbsf) may be attributed to the transition to the Flandrian.