The biostratigraphic results obtained for the continuously cored sequence at ODP Site 982 agree well with the spot-cored intervals at DSDP Site 116. The identification of the Bolboforma zones permits the correlation as shown in Figure 2, where Holes 982A, 982B, and 116 are equated to mbsf. The short intervals containing the different Bolboforma zones at Site 116 occur at depths similar to those at Site 982, with the exception of the determination of the B. danielsi Zone in Sample 12-116-9-1, 51-55 cm, at 459.53 mbsf. A 23-m downhole contamination may be the reason for this discrepancy. Based on the results obtained for Hole 982B, at Site 116 the B. costairregularis Zone as well as the B. reticulata Zone will subdivide into an upper and a lower part.
The distribution of 52 Bolboforma species in Neogene sediments at the Hatton-Rockall Basin is outlined in Table 1, Table 2, Table 3, Table 4, and Table 5. The various assemblages reflect 14 Bolboforma zones/subzones spanning the early Miocene to late Pliocene interval. Figure 3 summarizes the stratigraphic range of 30 well-defined Bolboforma index species, which are common and easy to recognize. Also shown are the determined Bolboforma zones and their correlation with nannoplankton and planktonic foraminifer biostratigraphy at the Hatton-Rockall Basin. These biostratigraphies are correlated with the standard nannoplankton zonations as well as with the time scale of Berggren et al. (1995).
The Matuyama/Gauss paleomagnetic event (with an age of 2.581 Ma, according to Berggren et al., 1995) is determined at the Hatton-Rockall Basin in Hole 982B at 52.55 mbsf (Jansen, Raymo, Blum, et al., 1996). The LO of the genus Bolboforma lies at 59.31 mbsf (Sample 162-982B-7H-5, 31 cm). This is located 6.76 m below the Matuyama/Gauss event. In accordance with the age/depth curve (Jansen, Raymo, Blum, et al., 1996), the LO of Bolboforma can be dated at 2.84 Ma, ~0.6 Ma younger than previously known (Spiegler and von Daniels, 1991).
The following events define the stage/substage boundaries. The late/early Pliocene boundary at 3.5 Ma is defined by the FO of Bolboforma elegans. The Pliocene/Miocene boundary at 5.3 Ma lies near the FO of B. costairregularis costairregularis at 5.61 Ma and the LO of B. intermedia at 5.68 Ma. The late/middle Miocene boundary is defined by the NN9/NN8 (CN7/CN8) nannoplankton zonation and the B. capsula/B. subfragoris zonal boundaries according to Spiegler and Müller (1992), and it is dated according Berggren et al. (1995) at 10.6 Ma. The middle/early Miocene boundary lies tentatively at the base of the B. reticulata Zone at 17.5 Ma.
The succession of the Bolboforma zones in the Neogene sediments at the Hatton-Rockall Basin agrees with that described by Spiegler and von Daniels (1991) and Spiegler (in press b). Moreover, the LOs and FOs of different and additional Bolboforma species give further zonal subdividing potential.
Excellent regionally widespread marker species with a short TR are B. danielsi, B. atlantica, and B. polygonalis. The TR of B. danielsi, identified in Hole 982B between 436.89 and 438.20 mbsf, characterizes a horizon dated to ~12 Ma at several sites in the North Atlantic (Spiegler and von Daniels, 1991; Spiegler and Müller, 1992; Spezzaferri and Spiegler, 1998) and also in the shelf area of northern Europe (Spiegler and von Daniels, 1991; Spiegler and Rusbült, 1994; Spiegler and Gürs, 1996; Gürs and Spiegler, in press). The TR of B. atlantica, observed in Hole 982B between 432.39 and 433.89 mbsf, lies above the TR of B. danielsi at the Rockall Basin as well as at the Reykjanes Ridge (Spiegler and Müller, 1992) and in the South Atlantic at the Meteor Rise (Spiegler and von Daniels, 1991). The TR of B. polygonalis in Hole 982B from 287.57 to 292.49 mbsf lies in the upper B. metzmacheri Zone. This short interval is also documented in the B. metzmacheri Zone in the Nieder Ochtenhausen well, drilled in northwest Germany (Spiegler, in press a).