At Site 1101, 217.7 m of Pleistocene and Pliocene hemipelagic silty clays was recovered. Four microfossil groups were present. Calcareous nannofossils and foraminifers were found in the uppermost core as well as in the more biocalcareous interval from 50 to 134 mbsf (approximately Unit II; "Lithostratigraphy"). Siliceous microfossils, diatoms and radiolarians, were found throughout the hole and became more abundant in the lowest three cores.

Diatom preservation and abundance varied in Hole 1101A. Intervals of abundant to common, well-preserved diatoms alternated with barren ones. Fragmentation of valves is common in the upper 160 m of Hole 1101A. Diatoms were more abundant in samples below Core 178-1101A-19X than in the upper part of the hole. The lowest three cores (Cores 178-1101A-22X, 23X, and 24X) contained a diverse, open-marine assemblage. All zones from the Pleistocene to the late Pliocene were identified at Site 1101 (Fig. F16). Table T3 lists the diatom datums noted at this site; datum intervals are listed with both their position within the cores and their depth (mbsf).

The Pleistocene species Hemidiscus karstenii was observed only in Core 178-1101A-3H, placing the first occurrence (FO) and last occurrence (LO) of this species within this core. The LO of Actinocyclus ingens was seen in Sample 178-1101A-3H-4, 110 cm (79.5 mbsf), defining the upper boundary of the A. ingens Zone. The LO of Fragilariopsis barronii is well defined in Sample 178-1101A-7H-1, 75 cm (48.6 mbsf). The next older zone is the Thalassiosira kolbei Zone. The species datum that defines the upper boundary of this zone (LO T. kolbei) was not observed within this hole. Thalassiosira torokina, with an LO datum of approximately the same age, was noted in Sample 178-1101A-14H-4, 44 cm (119.14 mbsf), and was used as a proxy for drawing a tentative upper zonal boundary.

The boundary between the T. kolbei and Thalassiosira vulnifica Zones is defined by the LO of T. vulnifica, which was seen in Sample 178-1101A-18X-CC (160.12 mbsf). The LO of Thalassiosira insigna, marking the top of the T. insigna/T. vulnifica Zone, was observed in Sample 178-1101A-20X-3, 70 cm (173.4 mbsf). Occurring slightly higher than the published age would place it, the LO of Fragilariopsis interfrigidaria was noted in Sample 178-1101A-19X-2, 70 cm (162.3 mbsf). The sample interval 178-1101A-21X-3, 58 cm (182.88 mbsf), through 21X-4, 40 cm (184.2 mbsf), contained two datums: the LO of Thalassiosira striata and the FO of T. vulnifica. These datums placed the top of the F. interfrigidaria Zone in Sample 178-1101A-21X-4, 40 cm (184.2 mbsf). One more datum was observed above the base of the core, the FO of T. insigna in Sample 178-1101A-23X-1, 29 cm (198.79 mbsf).

Radiolarian assemblages from core-catcher samples at Site 1101 contained both robust- and thin-shelled specimens. The sharp difference in shell thickness can be used to distinguish reworked and in situ assemblages, improving confidence in the identification of zonal boundaries. Reworked late Pliocene assemblages are present in the Pleistocene part of the section. In general, radiolarians are abundant and moderately preserved, with only two barren intervals (Fig. F16).

The youngest zone observed was the Psi Zone, indicated by the presence of Stylatractus universus and Antarctissa cylindrica. These specimens are lightly silicified and co-occur with robust tests of Triceraspyris antarctica, which are considered reworked. The bottom marker of the Psi Zone, Pterocanium charybdeum trilobum, is frequently rare and difficult to locate (Hays and Opdyke, 1967; Lazarus, 1990). It was not observed at Site 1101. However, Chen (1975) suggested using the top occurrence of Saturnalis circularis as the zonal marker between the Psi and Chi Zones. Although it is found rarely in Antarctic sediments (Lazarus, 1990), this species does occur at Site 1101 and is used to locate the bottom of the Psi Zone at 38 mbsf. The youngest observed occurrence of Cycladophora pliocenica coincides with this depth, supporting this conclusion.

The top occurrence of Eucyrtidium calvertense at 143 mbsf (Sample 178-1101A-16H-CC) marks the boundary between the Chi and Phi Zones. The base of the Phi Zone is placed at the first observed occurrence of Helotholus vema at 160 mbsf (Sample 178-1101A-18X-CC). The top occurrences of Desmospyris spongiosa and Prunopyle titan, two robust species, are difficult to locate because of reworking at this site and their resistance to breakage. The base of the hole is within the Upsilon Zone.

Calcareous nannofossils were recovered in some cores from Site 1101. Intervals of good preservation were confined to the uppermost two cores and Cores 178-1101A-9H through 14H. Nannofossils were also seen in samples from within the dominantly siliceous intervals but in low numbers and usually partly dissolved. Several samples (178-1101A-9H-4, 87 cm [69.1 mbsf]; 11H-4, 70 cm [90.9 mbsf]; and 12H-3, 63 cm [98.9 mbsf]) contained abundant Coccolithus pelagicus.

Three zones were recovered, and three datums were observed. The FO of Emiliania huxleyi was noted in Sample 178-1101A-2H-5, 90 cm (15.6 mbsf), defining the base of the CN15/NN21a Zone. From Cores 178-1101A-2H through 9H, only a few, rare specimens were observed, and they provided no age constraints. Pseudoemiliania lacunosa appeared in Sample 178-1101A-9H-4, 87 cm (69.1 mbsf), indicating a transition to the CN14b/NN19 Zone. This "event" was not the LO datum of P. lacunosa because of the presence of the barren interval confining it above. Within the CN14b/NN19 Zone, two datums and one time marker were noted. The LO of the large Gephyrocapsa spp. was seen in Sample 178-1101A-11H-4, 70 cm (90.9 mbsf), and the FO of this same form was observed at the base of Core 178-1101A-11H in the core-catcher sample (95.2 mbsf). Within Core 178-1101A-11H, Helicosphaera selli was noted but in such low numbers that the LO cannot be placed. What it does establish is that Core 178-1101A-11H is older than 1.25 Ma. Below Sample 178-1101A-14H-5, 90 cm (121.1 mbsf), calcareous nannofossils are rarely observed, as noted above.

At Site 1101, core catchers and many additional core samples were examined for foraminifers. Planktonic and both calcareous and agglutinated benthic foraminifers are present. Planktonic foraminifers are abundant to rare in the upper 134 mbsf of Site 1101. Foraminifer-rich sediments are most common from Sample 178-1101A-7H-5, 130-132 cm (55 mbsf), through Sample 178-1101A-16H-1, 80-83 cm (34 mbsf). There is only one carbonate-rich layer above this depth in Sample 178-1101A-1H-CC (8.6 mbsf) (see "Lithostratigraphy"). In these samples, more than 90% of the assemblage consists of Neogloboquadrina pachyderma sinistral, with rare 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 were not observed at Site 1101.

Benthic foraminifers are common within the foraminifer-rich sediments and rare in other samples from Site 1101. Deep-water species are more common than the reworked shallow-water species observed at Site 1096. Calcareous benthic foraminifers include Nuttallides umbonifer, Oridorsalis umbonatus, Cibicidoides mundulus, Pyrgo murrhina, Fontbotia wuellerstorfi, and Epistominella exigua. Agglutinated foraminifers, including Martinottiella antarcticus and Karreriella spp., occur rarely in the biosiliceous intervals.