Site 1168 (water depth = 2463 m) is located 70 km west of the Tasmanian coast on the continental slope of the Tasmanian western margin and is north of the STF (Fig. F1). A total of 837 m of sediment (average recovery = 94.7%), ranging in age from Pleistocene to late Eocene, was penetrated in Hole 1168A; a total of 20 m of Pleistocene sediment was recovered. Well to moderately preserved calcareous nannofossils are abundant throughout the Pleistocene section. Reworked early Miocene nannofossils were noted throughout the Pleistocene interval. Stratigraphic distribution of calcareous nannofossils from Hole 1168A is presented in Table T1. Key marker events are listed in Table T5 along with their corresponding zones and ages.
Sample 189-1168A-1H-1, 15–16 cm (0.15 meters below seafloor [mbsf]), to the top of the core represents the Emiliania huxleyi acme Zone, with abundant E. huxleyi and small Gephyrocapsa spp. This zone is based on the dominance of E. huxleyi relative to small Gephyrocapsa spp. and was easily recognizable at this sampling resolution without quantitative analysis. Other common species include Helicosphaera carteri, Pontosphaera japonica, and Calcidiscus leptoporus.
The Emiliania huxleyi Zone is based on the FO of E. huxleyi (0.24 Ma) and extends from Samples 189-1168A-1H-1, 90–91 cm (0.90 mbsf), to 1H-2, 15–16 cm (1.65 mbsf). Very abundant small Gephyrocapsa spp., abundant E. huxleyi, and common C. leptoporus and Coccolithus pelagicus characterize the nannofossil assemblage.
Samples 189-1168A-1H-2, 90–91 cm (2.40 mbsf), to 1H-3, 15–16 cm (3.15 mbsf), are assigned to the Gephyrocapsa oceanica Zone. This interval zone is characterized by the absence of both E. huxleyi and Pseudoemiliania lacunosa. Common nannofossils include C. leptoporus, C. pelagicus, H. carteri, P. japonica, and abundant small Gephyrocapsa spp.
The base of the Pseudoemiliania lacunosa Zone was defined by Gartner (1977) on the dominance reversal from small to larger gephyrocapsids. As larger gephyrocapsids are not consistent in their distribution throughout the study area, the LO of R. asanoi (0.83 Ma) is used to approximate this boundary. The LO of R. asanoi occurs between Samples 179-1168A-2H-2, 15 cm, and 2H-2, 90 cm (9.32 mbsf). Reworked specimens of R. asanoi above this interval were identified by their degraded preservational state. Dominant species include C. leptoporus, C. pelagicus, small Gephyrocapsa spp., H. carteri, P. lacunosa, P. lacunosa ovata, and small Reticulofenestra spp.
The small Gephyrocapsa Zone extends from Samples 189-1168A-2H-2, 90–91 cm (9.70 mbsf), to 2H-3, 15–16 cm (10.45 mbsf), based on the LO of H. sellii. Species diversity increases in this zone with common C. leptoporus, C. pelagicus, G. caribbeanica, small Gephyrocapsa spp., H. carteri, P. lacunosa, P. lacunosa ovata, and R. asanoi. Reworking of several species was noted throughout this zone (Table T1).
Sample 189-1168A-2H-3, 90–91 cm (11.20 mbsf) contains both H. sellii and C. macintyrei, placing this sample in the Calcidiscus macintyrei Zone. The FO of R. asanoi also occurs at this level, indicating a hiatus of ~0.4 m.y. encompassing the base of the small Gephyrocapsa Zone and the entire Helicosphaera sellii Zone (Fig. F3). The FO of G. caribbeanica was noted at ~14.5 mbsf, within the Calcidiscus macintyrei Zone, and is used here to approximate the base of the Pleistocene.
Discoaster brouweri, the traditional nannofossil marker of the Pliocene/Pleistocene boundary, was not common in the Pliocene sediments of Hole 1168A (Shipboard Scientific Party, 2001b) and was not encountered in the samples studied. The first downhole discoasterid encountered was Discoaster surculus (2.51 Ma) at ~20 mbsf. This event (LO of D. surculus) along with the FO of G. caribbeanica indicates a possible condensed section across the Pliocene/Pleistocene boundary (Fig. F3). The Pliocene/Pleistocene boundary could not be further constrained by other biomagnetostratigraphic events (Stickley et al., this volume).
Site 1170 (water depth = 2704 m) is located 400 km south of Tasmania on the western section of the STR and lies in subantarctic waters between the STF and the Subantarctic Front (SAF) (Fig. F1). Approximately 380 m of core (average recovery = 81.8%), ranging in age from Pleistocene to middle Eocene, was recovered from Hole 1170A. Calcareous nannofossils are abundant and well to moderately preserved throughout the studied section. Stratigraphic distribution of calcareous nannofossils from Hole 1170A is presented in Table T2. Table T5 lists key marker events with their corresponding depths and ages.
The Emiliania huxleyi acme Zone extends from Sample 189-1170A-1H-1, 60–61 cm (0.60 mbsf), to the top of the core. Within this interval, E. huxleyi is more abundant than small Gephyrocapsa spp. Other abundant species include C. pelagicus and small Reticulofenestra spp.
The base of the Emiliania huxleyi Zone is defined by the FO of E. huxleyi and extends to Sample 189-1170A-2H-1, 60–61 cm (2.30 mbsf). The nannofossil assemblage is characterized by abundant small Gephyrocapsa spp. and C. pelagicus as well as common to abundant E. huxleyi.
The Gephyrocapsa oceanica Zone, based on the absence of both E. huxleyi and P. lacunosa, continues down to Sample 189-1170A-2H-7, 60–61 cm. The base of this zone is defined by the LO of P. lacunosa (11.55 mbsf). Common nannofossils include C. leptoporus, H. carteri, small Gephyrocapsa spp., and abundant C. pelagicus. Reworking of C. macintyrei, H. inversa, H. sellii, and R. asanoi was rarely noted in this interval.
The base of the Pseudoemiliania lacunosa Zone is approximated by the LO of R. asanoi at 15.05 mbsf (between Samples 189-1170A-3H-3, 60–61cm, and 3H-3, 110–111 cm). Dominant species within this zone include C. pelagicus, small Gephyrocapsa spp., H. carteri, and small Reticulofenestra spp.
The small Gephyrocapsa Zone extends down to Sample 189-1170A-4H-5, 60–61 cm (26.55 mbsf), based on the LO of H. sellii. Common species in this zone are C. leptoporus, C. pelagicus, small Gephyrocapsa spp., H. carteri, R. asanoi, and small Reticulofenestra spp.
The Helicosphaera sellii Zone is represented by one sample: Sample 189-1170A-4H-5, 60–61 cm. The base of this zone is defined by the LO of C. macintyrei (26.8 mbsf), which is also used to approximate the Pliocene/Pleistocene boundary in Hole 1170A. Abundant small Reticulofenestra spp. and common C. macintyrei, C. leptoporus, C. pelagicus, and small Gephyrocapsa spp. characterize the Calcidiscus macintyrei Zone.
The Pliocene/Pleistocene boundary could not be more tightly constrained by nannofossils, as discoasterid species were not present in the upper Pliocene sediments (Shipboard Scientific Party, 2001d) and were not located by detailed shorebased examination (Table T2). The FOs of G. caribbeanica and G. oceanica were also not used to constrain the boundary, as their distribution was discontinuous. However, the Pliocene/Pleistocene boundary can be further constrained in Hole 1170A by the diatom LO of Simonseniella barboi (1.8 Ma) and the onset of Chron C2n (1.95 Ma) (Stickley et al., this volume).
Site 1171 is located in 2148 m of water over the central STR and east of the Balleny Fracture Zone; it lies in subantarctic waters between the STF and the SAF (Fig. F1). Approximately 120 m of core (average recovery = 94%) was recovered in Hole 1171A (Shipboard Scientific Party, 2001e). Pleistocene nannofossils are well to moderately preserved and abundant. Stratigraphic distribution of calcareous nannofossils is listed in Table T3, with key marker events listed in Table T5.
Sample 189-1171A-1H-1, 15–16 cm (0.15 mbsf), to the top of the core, represents the Emiliania huxleyi acme Zone. Emiliania huxleyi is more abundant than small Gephyrocapsa spp., although both dominate the assemblage. Calcidiscus leptoporus, H. carteri, Pontosphaera spp., and small Reticulofenestra spp. are also present.
The lower boundary of the Emiliania huxleyi Zone is based on the FO of E. huxleyi. The zone extends to Sample 189-1171A-1H-2, 90–91 cm (2.40 mbsf). The assemblage is characterized by very abundant small Gephyrocapsa spp., abundant E. huxleyi and C. pelagicus, and common C. leptoporus. Reworked P. lacunosa were noted at the base of this zone.
Samples 189-1171A-1H-3, 15–16 cm (3.15 mbsf), to 1H-5, 90–91 cm (6.90 mbsf), are assigned to the Gephyrocapsa oceanica Zone. The base of this zone is identified by the LO of P. lacunosa. Common to abundant C. leptoporus and C. pelagicus and abundant small Gephyrocapsa spp. and small Reticulofenestra spp. characterize this interval.
The base of the Pseudoemiliania lacunosa Zone is approximated by the LO of R. asanoi between Samples 189-1171A-2H-4, 90–91 cm, and 2H-5, 15–16 cm (12.88 mbsf). The FO of Gephyrocapsa parallela was used by Gartner (1977) to define the base of this zone but was only observed in two samples in Hole 1171A. Assemblage species include C. pelagicus, small Gephyrocapsa spp., H. carteri, P. lacunosa ovata, and small Reticulofenestra spp.
The small Gephyrocapsa Zone extends down to ~21 mbsf (Sample 189-1171A-3H-3, 90–91 cm), where the LO of H. sellii was noted. Species diversity increases within this zone with abundant C. leptoporus, C. pelagicus, small Gephyrocapsa spp., H. carteri, P. lacunosa, P. lacunosa ovata, and small Reticulofenestra spp. The FO of R. asanoi occurs within this zone.
The base of the Helicosphaera sellii Zone is defined by the LO of C. macintyrei at ~23 mbsf (between Samples 189-1171A-3H-5, 15–16 cm, and 3H-5, 90–91 cm). The Helicosphaera sellii Zone is represented by three samples in Hole 1171A, with H. sellii rare and discontinuous at the top of this zone.
As at Site 1170, the Pliocene/Pleistocene boundary could not be determined by nannofossils, as D. brouweri was not reported in the upper Pliocene sediments (Shipboard Scientific Party, 2001e), nor was it recorded by this study (Table T3). The Pliocene/Pleistocene boundary can be constrained by the LO of C. macintyrei (1.59 Ma); the LOs of diatoms Fragilariopsis barronii (1.4 Ma), Thalassiosira tetraoestrupii var. reimeri (1.5 Ma), Proboscia barboi (1.8 Ma); and the termination of Chron C2n (1.77 Ma) and onset of Chron C2n (1.95Ma). The Pliocene/Pleistocene boundary, defined by the termination of Chron C2n (1.77 Ma), is placed at ~24 mbsf (Stickley et al., this volume).
Site 1172 lies on the flat western side of the ETP, just north of the STF and under the influence of the East Australian Current (EAC) in cool, temperate waters (Fig. F1). Approximately 480 m of sediment (recovery = 93%) was recovered in Hole 1172A. Calcareous nannofossils are abundant and well to moderately preserved throughout the study section. Preservational indicators range from intact coccospheres in well-preserved assemblages to little u's (individual placolith elements) in moderately preserved assemblages (Hay and Beaudry, 1973). Stratigraphic distribution of calcareous nannofossils is listed in Table T4. Key marker events are listed in Table T5 with corresponding ages and depths.
Sample 189-1172A-1H-1, 15–16 cm (0.15 mbsf), to the top of the core represents the Emiliania huxleyi acme Zone, with E. huxleyi dominant to small Gephyrocapsa spp. Common nannofossil species include C. leptoporus, C. pelagicus, and small Reticulofenestra spp., with few H. carteri.
The Emiliania huxleyi Zone extends down to Sample 189-1172A-1H-2, 15–16 cm, defined by the FO of E. huxleyi. Very abundant small Gephyrocapsa spp. and common E. huxleyi, C. leptoporus, and C. pelagicus characterize the nannofossil assemblage.
Samples 189-1172A-1H-2, 117–118 cm (2.67 mbsf), through 2H-1, 15–16 cm (6.45 mbsf), represent the Gephyrocapsa oceanica Zone. The base of this interval zone is defined by the LO of P. lacunosa. The assemblage includes common C. leptoporus, common to abundant C. pelagicus, few to common G. caribbeanica and G. oceanica, and abundant small Gephyrocapsa spp. and small Reticulofenestra spp. Reworked specimens of D. brouweri and H. inversa were noted in this interval.
The base of the Pseudoemiliania lacunosa Zone is approximated at Site 1172 by the LO of R. asanoi at ~9 mbsf (Sample 189-1172A-2H-2, 117–118 cm). Abundant species include small Gephyrocapsa spp. and small Reticulofenestra spp., with common H. carteri, C. pelagicus, and C. leptoporus.
The small Gephyrocapsa Zone extends down to Sample 189-1172A-3H-3, 15–16 cm, based on the LO of H. sellii. Species are diverse with common to abundant C. leptoporus, C. pelagicus, small Gephyrocapsa spp., and small Reticulofenestra spp., H. carteri, and P. lacunosa.
Sample 189-1172A-3H-3, 117–118 cm (19.97 mbsf), contains both H. sellii and C. macintyrei, placing this sample in the Calcidiscus macintyrei Zone. The concurrent appearance of both species indicates a hiatus of ~0.3 m.y. encompassing the Helicosphaera sellii Zone. The Pliocene/Pleistocene boundary is defined by the LO of D. brouweri (1.95 Ma) and is placed between Samples 189-1172A-3H-7, 15–16 cm, and 3H-CC (~25.25 mbsf). The Calcidiscus macintyrei Zone is characterized by C. leptoporus, C. pelagicus, small Gephyrocapsa spp., small Reticulofenestra spp., and few C. macintyrei, H. carteri, P. japonica, and P. lacunosa.