Many of the index species for the Oligocene-Miocene in northwestern Europe have not been recorded from the Norwegian Sea. This has been a handicap for palynological studies on cores from previous DSDP/ODP legs in the Norwegian-Greenland Sea since the first cruise to these waters in 1974 (DSDP Leg 38; Manum, 1976). Nevertheless, for the age determinations shown in Table 2 and Figure 3 for Hole 985A, we were able to use several dinocyst species with well-documented ranges and for which there is independent stratigraphic (usually nannofossil or planktonic foraminiferal) control outside the Norwegian Sea. The other dinocyst taxa used for age determination belong to formal and informal taxa that have restricted ranges in the Norwegian Sea, particularly in cores from Leg 104, Site 643 (Manum et al., 1989, and others), but have seldom been recorded outside the area. We found these taxa helpful in correlation with Site 985.
For correlation between Site 985 and Site 643, we have used the chronostratigraphic framework established for the Norwegian-Greenland Sea sites by Goll (1989) in his comprehensive biostratigraphic synthesis for Leg 104. This has recently been modified (R. M. Goll, unpubl. data), and we are using the new version for this study. In Figure 4 (center column), the ages assigned by Goll to the Miocene cores from Site 643 are shown using the time scale of Berggren et al. (1995). These ages are based on evidence from several microfossil groups, except for the earliest part of the Miocene (Cores 104-643A-42X through 31X) where dinocysts provide the only biostratigraphic control (Manum et al., 1989). Core 104-643A-43X has a NP25 nannofossil marker (Discolithina enormis) and is referred to by Goll as the late Oligocene. The age of Core 42X is in dispute: the dinocysts indicated an early Miocene age, whereas Goll considered it Oligocene. Independent stratigraphic control is also lacking for the Oligocene interval below Core 104-643A-43X, and the early Oligocene age indicated for Cores 47X through 50X is also contentious. The dinocyst range chart for Site 643 (Manum et al., 1989) shows a clear break between Cores 104-643A-46X and 47X, which supports Goll's interpretation of a major hiatus.
First and last occurrences of stratigraphically useful species are shown in Table 2. Many of the taxa listed are informal, being known from previous dinocyst studies on Norwegian Sea cores; four informal taxa (Lophocysta sp. 1 and sp. 2, Eatonicysta sp. 1, Gen. et sp. indet.; see below under "Informal Taxa with Restricted Stratigraphic Ranges") are introduced in this study. For the taxonomy of formal species, we follow Lentin and Williams (1993).
Samples from Hole 985A, Cores 62X through 58X (which we regard as Oligocene), contain several taxa that first occur in the Oligocene of northwestern Europe. These are Areoligera semicirculata, Artemisiocysta cladodichotoma, Phthanoperidinium filigranum, Reticulatosphaera actinocoronata, and Spiniferites mirabilis. Apteodinium spiridoides, which occurs in Section 162-985A-60X-5, has never been recorded from pre-Rupelian sediments. The oldest known occurrence is 31.50 Ma (within the Rupelian), according to Stover and Hardenbol (1993). The presence of Svalbardella cooksoniae in Section 162-985A-59X-2 also supports a Rupelian age for the lowermost part of the hole. The last occurrence of Areoligera semicirculata in Section 162-985A-51X-2 upholds our interpretation of a Rupelian age for the interval from Core 162-985A-62X through Section 51X-2 because this species is restricted to the Rupelian (Williams et al., in press). Accordingly, the sample from Section 60X-5 is taken as no older than Rupelian. Section 50X-5 is tentatively included in the Chattian, on the basis of the last occurrence of Spiniferella cornuta, which, from Benedek (1972), has its youngest known occurrence at 27 Ma. This may represent the top of the Oligocene. Section 162-985A-48X-6, which contains Chiropteridium galea, is questionably included in the Aquitanian. The last occurrence of C. galea was taken to mark the top Oligocene at Sites 643 and 908. However, in the eastern United States, de Verteuil and Norris (1996) recorded this taxon in the earliest Miocene. Following these authors, we have questionably included Section 162-985A-48X-6 in the early Miocene. Our age determination implies that there is a major hiatus within the Chattian, which agrees with the boundary between lithostratigraphic Units V and IV in Section 162-985A-50X-2, which is considered the Oligocene/Miocene boundary. Section 162-985A-48X-4 is interpreted as early Miocene on the basis of the presence of Leptodinium sp. III of Manum (1976), which is known only from the Miocene.
We consider the interval from Section 162-985A-48X-4 to our uppermost sample in Section 162-985A-32X-1 to be early Miocene in age. The Aquitanian/Burdigalian boundary is placed between Sections 162-985A-37X-5 and 36X-5. Section 162-985A-37X-5 contains Evittosphaerula paratabulata, which at Site 643 first appears in Section 162-985A-34X-2, dated as 21 Ma by R.M. Goll (unpubl. data; Fig. 3). Lophocysta sulcolimbata first appears at Site 643 in Section 162-985A-32X-1, which is taken to be 20.5 Ma. Because the Aquitanian/Burdigalian boundary is 20.52 Ma, this indicates that Section 37X-5 is Aquitanian and Section 36X-5 is Burdigalian.
We consider Section 162-985A-32X-1, our uppermost sample, to be no younger than the Burdigalian because it contains Nematosphaeropsis downiei. Brown (1986) recorded this species from the early Miocene of Hole 548A in the Bay of Biscay. Powell (1986b) recorded it as Nematosphaeropsis? sp. A, from the lower Miocene of Italy.
The conjugate position of Sites 985 and 643, with respect to the spreading axis, makes it reasonable to assume that the evolution of the basin was similar at both sites. This is confirmed by the correspondence between the succession of dinocyst events shown for the Oligocene and lower Miocene sections of both sites (Fig. 4).
In Figure 4, we show the first and last occurrences of dinocysts that appear to be of stratigraphic significance at Site 985 and correlation with the same events at Site 643. The sequence of events in the two core holes is similar, particularly for taxa that appear to be endemic to the Norwegian Sea. The few taxa that do not fit are mostly species that also occur outside the Norwegian Sea. These taxa may well have distributions that are at variance with the endemic ones; they may be warmer water species showing erratic occurrences because of periodic migration into the higher latitudes. Another factor that may have influenced migration of lower latitude taxa is the Iceland-Faeroe Ridge, which was an obstacle to water-mass circulation and migration between the Norwegian Sea and the North Atlantic until well into Miocene times. The last occurrence of Cordosphaeridium cantharellum at the two sites does not follow the general pattern, being stratigraphically lower in Hole 985A. Its last occurrence at Site 643 may be reworked; its last consistent occurrence in that hole is in Section 162-643A-28X-7, which is in agreement with its last occurrence at ~18 Ma in northwestern Europe. Apteodinium australiense is another example of a species with a different range. Apteodinium australiense has its last occurrence in the Norwegian Sea in sediments older than in northwestern Europe, where it has been recorded from the middle Miocene (Serravalian). An endemic taxon that does not fit the pattern is Leptodinium sp. III. Its base may not have been noted in the core at Site 643 because it is rare and probably inconsistently identified.
A comparison of early Miocene events shows particularly good agreement between the intervals from Sections 40X-2 to 35X-1 of Site 985 and from Sections 41X-1 through 31X-2 of Site 643. The correlation of these intervals has implications for the interpretation of the early Miocene at these sites. A section equivalent to Cores 48X-41X at Site 985 appears to be missing at Site 643 because there is independent evidence for the NP25 zone in Core 104-643A-43X (but not 42X). Also, Core 162-985A-48X is considered by us to be early Miocene because of the presence of Leptodinium sp. III Manum, 1976. The occurrence of Leptodinium sp. III in Core 33X at Site 643 indicates a more complete lower Miocene section at that site.
Goll's (1989; R.M. Goll, unpubl. data) interpretation of an Oligocene hiatus is supported by our correlation of events. At Site 985, the hiatus comprises most of the Chattian, and the correlation between events in the sections below the hiatus at both sites indicates a similar time span for the hiatus at Site 643. The correlation also indicates a much thicker Rupelian section at Site 985, which is reasonable considering that it was much closer to a continental sediment source in the Oligocene.
The palynological study of the first DSDP leg to the Norwegian Sea (Leg 38; Manum, 1976) revealed many new and distinctive dinocyst taxa with restricted ranges. Time constraints did not allow description of these taxa; thus, they were only illustrated and informally named. A few of these taxa have since been described (i.e., Evittosphaerula paratabulata and Lophocysta sulcolimbata in Manum, 1979, and Unipontidinium [as Nematosphaeropsis] aquaeductum in Piasecki, 1980), but most still remain informal. The same nomenclature was applied in the dinocyst study of Leg 104 cores (Manum et al., 1989). Because the Leg 104 holes were continuously cored in contrast to the spot coring practiced during Leg 38, the stratigraphic ranges of many of these informal taxa were determined more precisely. New taxa with restricted ranges were also recorded, illustrated, and reported under open taxonomy. In the present study, many of these informal taxa have proved useful in correlating Site 985 with Site 643 and dating the Oligocene-lower Miocene section. In addition to the taxa in Table 2, we recorded a few others with restricted ranges. They all have distinctive morphologies, so that good illustrations suffice for identification. Given their restricted ranges in the Norwegian Sea, we are convinced that these taxa will be useful for future stratigraphic studies in the northernmost Atlantic. To facilitate identification, we present brief comments on taxa and include illustrations.
Batiacasphaera
baculata sensu Manum et al., 1989
(pl. 1, fig. 9; not pl. 1, fig. 8); Plate 2,
figure 8
= cf. Batiacasphaera baculata Manum, 1976 (pl. 2, fig. 25)
= "Kallosphaeridium biornatum group" of Heilmann-Clausen and Costa, 1990 (pl.
19, figs. 1, 5, 6)
This is a peridinioid cyst that, according to Damassa (1997), has a 3A3I archeopyle (also see illustration in Manum, 1976). It is therefore not related to Batiacasphaera. The thin autophragm has scattered rods on the surface. The form shown in Manum et al. (1989, pl. 1, fig. 8) is morphologically related, but the ornamentation is rounded warts rather than rods. The base is in Section 162-985A-40X-2 (104-643A-41X-1); the top is in Section 162-985A-34X-2 (104-643A-24X-5).
Deflandrea
sp. B Powell 1986b sensu Manum et al., 1989
(pl. 9, fig. 7); Plate 2, figure 7
This form is characterized by its overall corroded appearance. The periphragm is often only partially preserved or missing. The endophragm is coarsely granular to spongy and has an appearance of being in various states of dissolution. Deflandrea sp. B has a consistent occurrence and is typically common to frequent in relative abundance. It seems to be closely related to Deflandrea leptodermata, which was originally recorded from the upper Eocene (Cookson and Eisenack, 1965). The base is in Section 162-985A-62X-2 (104-643A-53X-3); the top is in Section 162-985A-53X-4 (104-643A-47X-4)
Eatonicysta sp. 1; Plate 2, figures 4, 5
This taxon has an ectophragmal network that is intermediate between Eatonicysta ursulae and Eatonicysta sequestra. The cysts are smaller than those of the other species. The tabulation has not been determined. This taxon is consistently present from Sections 162-985A-60X-2 through 51X-4, with some high relative frequencies. It is sporadic above, and probably reworked specimens occur in Section 162-985A-47X-4 and higher.
Hystrichokolpoma
sp. 2 Manum et al., 1989
(pl. 13, figs. 1, 2); Plate 2,
figure 3
(= Hystrichokolpoma reductum nom. nud. of Zevenboom, 1995)
This species of Hystrichokolpoma resembles Hystrichokolpoma rigaudiae but is devoid of cingular processes. The base is in Section 162-985A-36X-2 (104-643A-36X-5); the top is in Section 162-985A-35X-1 (104-643A-28H-7).
Leptodinium
sp. III Manum, 1976
(pl. 1, fig. 15); Plate 2, figure
6; Manum et al., 1989
(pl. 12, figs. 14, 15)
This taxon probably belongs to Impagidinium. Its distinctive features are rudimentary development of sutural ridges and short gonal processes. The base is in Section 162-985A-48X-4 (104-643A-33X-1); the top is in Section 162-985A-35X-6 (104-643A-31X-2).
Lophocysta sp. 1; Plate 1, figures 1-5
This differs from Lophocysta sulcolimbata in that the sulcal periphragm has perforations of greatly varying size, forming an irregular network and having some gonal processes up to 15 µm long. The base is in Section 162-985A-46X-4; the top is in Section 162-985A-41X-6.
Lophocysta sp. 2; Plate 1, figures 6-10
The endocyst is ovoidal, with a ventrally expanded and fenestrate periphragm attached to the endocyst laterally(?) by ribbonlike connections. The endocyst is ~30 µm × 45 µm, periphragm expansion two to three times the endocyst diameter. The archeopyle appears to be precingular. Ventral holes in the periphragm and holes in the ribbons are suggestive of plates, but sutures are lacking. Piccoladinium fenestratum Versteegh and Zevenboom (1995) resembles Lophocysta sp. 2 in its fenestrate periphragm but has parasutural features, and the sulcal fenestration appears different. This appears to be an extreme form of Lophocysta. The base is in Section 162-985A-62X-3; the top is in Section 162-985A-52X-1 (only in Section 104-643A-48X-6 of Hole; S.B. Manum, unpubl. data).
Pyxidinopsis
sp. 1 Manum et al., 1989
(pl. 3, fig. 7); Plate 2, figures
9A, 9B
The proximate cysts have a spherical shape, a diameter ~42 µm, and a large 3P archeopyle. The autophragm is only with a distinct reticulation, lumina are 1-2 µm across, and muri are ~1 µm high. The base is in Section 162-985A-54X-2 (104-643A-48X-1); the top is in Section 162-985A-32X-1 (104-643A-15X-6).
Spiniferites
sp. 1 Manum et al., 1989
(pl. 17, fig. 5); Plate 2, figure
10
The cyst body is 60-70 µm in diameter with rigid processes ~30 µm long and trifurcations up to 10 µm long. The cyst body is thick walled, rigid, and usually of dark brown color, with rugulate ornamentation forming an imperfect reticulum. The base is in Section 162-985A-62X-2 (104-643A-49X-4); the top is in Section 162-985A-60X-5 (104-643A-49X-3).
Dinocyst
3 Manum et al., 1989
(pl. 8, figs. 3, 4); Plate 2,
figures 1, 2
This form mimics an Evittosphaerula in having a periphragmal parasutural network. However, it has a dorsally attached endocyst and differs from Evittosphaerula in having only three apical plates and in not having the wide cingular plates. It is also quite small compared with Evittosphaerula; the overall diameter usually is <50 µm. Versteegh and Zevenboom (1995) included Evittosphaerula sp. 1 in synonymy with Piccoladinium fenestratum. However, there appear to be significant differences, such as the large anterior sulcal in Dinocyst 3. This would more closely link it to Evittosphaerula, which has the L-type ventral organization, than to Piccoladinium, which has the S-type ventral organization. The base is in Section 162-985A-62X-1 (104-643A-48X-6); the top is in Section 162-985A-59X-1 (104-643A-48X-5).
Gen. et sp. indet.; Plate 1, figures 11-15
The general shape of this taxon resembles a money belt. The subspherical endocyst (~20 µm × 35 µm) has a large periphragmal loop (diameter 65-75 µm) attached to it in lateral(?) positions. The loop or belt widens distally to ~15-20 µm and is U-shaped in cross section; it has a thickened marginal rim and adjoining thickenings suggestive of parasutures. The endocyst is delicate, making the archeopyle difficult to identify, but it appears to be precingular. The base is in Section 162-985A-56X-1; the top is in Section 162-985A-55X-4 (104-643A only in Section 48X-1; S.B. Manum, unpubl. data).
Extensive reworking of Paleogene taxa has created a problem throughout the section studied. We have therefore aimed at basing our analysis on first occurrences. Also, several Cretaceous taxa have been recorded. The Cretaceous taxa include Aptea polymorpha, Canningia colliveri, Chatangiella tripartita, Chichaouadinium vestitum, Circulodinium distinctum, Cribroperidinium orthoceras, Cymososphaeridium validum, Odontochitina costata, Palaeohystrichophora infusorioides, Pseudoceratium eisenackii, Pseudoceratium securigerum, and Subtilisphaera pellucid. The reworked Cretaceous dinocysts and spores occur throughout the section.