Compared to Site 1095, Site 1096 reveals both faster sedimentation and better biogenic preservation. Calcareous nannofossils appeared somewhat unexpectedly in material recovered from this site within the upper 174 mbsf. Below this depth, the biostratigraphy is based on the biogenic silica record. The change at 174 mbsf coincides with the lithologic change from Unit II to Unit III, which continues to the base of Hole 1096C (see "Lithostratigraphy"). The high sedimentation rate of this lower section has expanded the biostratigraphic zones to approximately three times their thickness at Site 1095. The bottom of Hole 1096C is believed to be early Pliocene in age.

Diatoms are generally rare to barren in sediments from Hole 1096A and the upper parts of Holes 1096B and 1096C. The exception to this is in brown, possibly interglacial, sediments found in the lower portion of Cores 178-1096A-2H and 178-1096B-2H and 3H, in which diatoms are common and the assemblage is dominated by Fragilariopsis kerguelensis, Thalassionema spp., and Thalassiothrix spp. fragments. The presence of Hemidiscus karstenii also suggests that those intervals are within the interval 0.19 to 0.49 Ma (Shipboard Scientific Party, 1999).

The zonal boundaries in the upper part of the diatom zonal scheme used on this leg are based on last occurrence (LO) datums. The zonal determinations for Holes 1096A, 1096B, and 1096C are shown in Figure F19. The extensive reworking that happens in glacial environments makes the task of identifying these datums more difficult. The sporadic Pliocene diatom species, including Thalassiosira torokina, T. inura, T. vulnifica, and T. oliverana with neritic diatom Paralia sulcata in Hole 1096A and the upper part of Holes 1096B and 1096C, was considered reworked because of the presence of well-preserved calcareous nannofossils of a younger age (<1.69 Ma). Table T3 summarizes the diatom datums for this site.

The co-occurrence of Thalassiosira complicata and T. inura without T. vulnifica in samples from Cores 178-1096B-21H, 22H, and 24H through 26X suggests placement of those samples in the Thalassiosira kolbei Zone. The upper zonal boundary marker species, T. kolbei, was not observed at this site. The topmost occurrence of T. vulnifica observed in Sample 178-1096B-23X-3, 70 cm (177.6 mbsf), defines the base of the T. kolbei Zone.

The presence of T. vulnifica and the absence of Thalassiosira insigna in Samples 178-1096B-27X-CC through 30X-1, 82 cm (242 mbsf), suggest placement of those samples in the T. vulnifica Zone. The LO of T. insigna, indicating the base of the T. vulnifica Zone, is noted between Samples 178-1096B-30X-1, 82 cm, and 30X-2, 72 cm (243.5 mbsf).

The co-occurrence of T. insigna and T. vulnifica in Samples 178-1096B-30X-2, 72 cm, through 32X-CC and Samples 178-1096C-7X-CC through 13X-1, 10 cm, implies that those samples are within the T. insigna/T. vulnifica Zone. The base of this zone is defined by the first occurrence of T. vulnifica in Sample 178-1096C-13X-1, 10 cm (308.9 mbsf).

The Fragilariopsis interfrigidaria Zone extends over the largest depth interval of any zone at this site, including 17 cores (from 178-1095C-30X through 14X). The base is defined by the first occurrence (FO) of F. interfrigidaria, in Sample 178-1096C-30X-CC (482.5 mbsf). The FO of Fragilariopsis barronii (base of the F. barronii Zone) is in Sample 178-1096C-37X-CC (550.3 mbsf). Two cores down, in Sample 178-1096C-40X-CC (579.1 mbsf), the base of the T. inura Zone is indicated by the FO datum of T. inura. Although the diatoms in Core 178-1096C-41X were not well preserved, they did not contain any T. inura, restricting the lowest part of the cored section to the Thalassiosira oestrupii Zone.

Radiolarians sampled at Site 1096 ranged in age from Pleistocene (Psi Zone) to early Pliocene (Tau Zone) (Fig. F19). The younger sediments were dominated by calcareous microfossils and lacked sufficient siliceous biogenic material to determine radiolarian zonal boundaries. In the upper Pliocene, below ~ 220 mbsf, preservation of radiolarians improved. This portion of the section down to the bottom of Hole 1096C is greatly expanded compared to Site 1095. Interestingly, a specimen of the subpolar-subtropical Dictyocoryne genus was found in Sample 178-1096A-21H-CC.

Because of the sparseness of fauna and absence of age-diagnostic species, Pleistocene to late Pliocene zones cannot be distinguished. The youngest discernible age is 0.610 Ma, suggested by the presence of Antarctissa cylindrica in Sample 178-1096A-4H-CC (36.2 mbsf). This implied an age of at least 0.610 Ma, placing it in the Psi Zone. From 36.2 to ~220 mbsf, no other biostratigraphic markers occur, preventing the determination of the Chi and Phi Zones.

The presence of Helotholus vema at 222 mbsf (Samples 178-1096A-27H-CC and 178-1096C-5X-CC) indicates an age of at least 2.421 Ma within the Upsilon Zone. The 50-m barren interval above 222 mbsf precludes the location of the upper boundary of the Upsilon Zone. Two events within the Upsilon Zone were noted at this site. The earliest observed appearance of Prunopyle titan (3.489 Ma) was at 232 mbsf; Lampromitra coronata (3.705 m.y.), at 531 mbsf. Both occur after 10-m barren intervals in which the actual top occurrences may exist. Neither the top (last occurrence datum [LOD]) of Desmospyris spongiosa nor the bottom (first occurrence datum) of Cycladophora davisiana was observed, even though these two events occur above the top (LOD) of P. titan. The assemblage within the Upsilon Zone is consistent downcore and similar to that observed at Site 1095. In the lower part of the section (Cores 178-1096C-13X through 38X, 308.8 to 559.8 mbsf), the >63-µm fraction was extremely diluted by mud. It contained common to abundant radiolarians and a small proportion of mineral grains, however.

Sample 178-1096C-38X-CC contains the lowest occurrence of H. vema, and the following core recovered no sediment. Consequently, we conclude that the boundary between the Upsilon and Tau Zones is in the interval from 560 to 570 mbsf (Core 178-1096C-39X). Abundance and preservation diminished from ~560 mbsf to the bottom of the hole. The top common occurrence of Lychnocanium grande (5.018 m.y.) was not encountered.

Occurrences of calcareous nannofossils were confined to the upper 170 m of Holes 1096A and 1096B (Fig. F19). The acme of Emiliania huxleyi that marks the base of the CN15/NN20 Zone was not observed. The youngest nannofossils allow a determination of the CN14b/NN19 Zone, with E. huxleyi present and Pseudoemiliana lacunosa absent. The base of this zone is in an interval barren of nannofossils, which extends to the lower portion of Core 178-1096A-6H. Below this depth P. lacunosa is a consistent but never dominant part of the assemblage, indicating the upper boundary of CN14a/NN19 at Sample 178-1096A-6H-CC (55.2 mbsf). Intermittent intervals of well-preserved calcareous nannofossils characterize the CN13b/NN19 Zone (see Fig. F19), bounded above by the reentry of the medium Gephyrocapsa spp. This zone continues from Sample 178-1096B-9H-6, 61 cm, to 22H-CC (78.3-174 mbsf), where occurrences of calcareous nannofossils begin. Below this depth in the hole, all observed samples are barren of well-preserved nannofossils. A few core-catcher samples contain very dissolved specimens of Coccolithus pelagicus and Sphenolithus spp., but they are never comparable in preservation to the assemblages from the upper sections.

The species C. pelagicus is a dominant member of assemblages in several samples (178-1096A-9H-6, 130 cm; 14H-1, 132 cm; 14H-2, 44 cm; 15H-5, 117 cm; 178-1096B-10H-1, 68 cm). Beaufort and Aubry (1992) suggested that Miocene fluctuations in C. pelagicus from Site 747 on the Kerguelen Plateau were dependent on water temperature. They note that C. pelagicus is a stenothermal species, adapted to temperatures ranging from 0° to 15°C, with optimal abundance between 2° and 12°C. They found five such intervals of increased C. pelagicus abundance in the Miocene but none from the Pliocene or Pleistocene.

At Site 1096, selected core catchers and many core samples were examined for foraminifers. Planktonic foraminifers are abundant to rare at Site 1096. In addition, both calcareous and agglutinated benthic foraminifers are present in small numbers. An unidentified species of Bolboforma is abundant in one core-catcher sample, 178-1096C-14X-CC (328 mbsf). The size and amount of the sand fraction containing foraminifers is highly variable at Site 1096. Some samples contain almost no sand, whereas others contain abundant, well-sorted, coarse or fine sand, or larger sized ice-rafted detritus. The most common lithologies of ice-rafted pebbles are basalts and green volcaniclastics. The abundance of foraminifers does not appear to be related to the amount of sand fraction, and foraminifers are present in equal numbers in both sand-rich and sand-poor samples. Beneath 350 mbsf, samples were indurated and difficult to process, and fewer samples were examined.

Planktonic foraminifers are present throughout Holes 1096A, 1096B, and 1096C. In the upper 174 mbsf, planktonic foraminifers are abundant to rare, but from 174 to 598 mbsf they are only rare. All samples contain Neogloboquadrina pachyderma sinistral (Fig. F19). In the upper interval there are several samples of foraminiferal ooze, including Samples 178-1096B-7H-1, 100-104 cm (52.3 mbsf); 178-1096A-14H-2, 47-49 cm (123.6 mbsf); and 178-1096B-20H-2, 134-136 cm (160.5 mbsf). In these samples, more than 90% of the assemblage consists of N. pachyderma sinistral with rare occurrences of N. pachyderma dextral and Globigerina bulloides, which is consistent with a Pleistocene to late Pliocene age for this interval (Pujol and Bourrouilh, 1991). Reworked planktonic foraminiferal faunas are present in several samples. Both Samples 178-1096B-12H-CC (108 mbsf) and 13H-CC (115.8 mbsf) contain excellently preserved middle to late Miocene planktonic foraminifers including Globoturborotalita woodi and Neogloboquadrina continuosa.

Benthic foraminifers are rare in scattered samples throughout Site 1096. Shallow-water shelf species, including Globocassidulina subglobosa, are more common than deep-water species. Only Sample 178-1096B-20H-2, 134-136 cm (160.5 mbsf), contains an excellently preserved deep-water benthic foraminiferal assemblage, including Nuttallides umbonifer, Oridorsalis umbonatus, Cibicidoides mundulus, and Epistominella exigua. Samples where siliceous microfossils were especially abundant, 178-1096C-7X-CC (262 mbsf), 28X-CC (464 mbsf), and 33X-CC (509 mbsf), contained agglutinated foraminifers, including Martinottiella nodulosa and Karreriella sp.