The combined cored sequence at Site 1168 (see Figs. F1, F2) (mainly Hole 1168A; total depth [TD] = 883.5 meters below seafloor [mbsf]) broadly consists of 260 m of nannofossil ooze of middle Miocene and younger age (lithostratigraphic Unit I); 400 m of clayey chalk, nannofossil siltstone, and sandstone of early Miocene and Oligocene age (Unit II); and 220 m of shallow-marine carbonaceous mudstone and sandstone (Units III-V) of late Eocene age (Shipboard Scientific Party, 2001b). Construction of a composite section of the triple-cored portion of the sedimentary sequence (~110 mbsf) indicates that there are no stratigraphic gaps to that depth. Beyond that, there are limited gaps, but overall core recovery averaged 93%. More details on lithology and sedimentology are available in the Leg 189 Initial Reports volume (Shipboard Scientific Party, 2001b).
Initial shipboard data and interpretation suggests that sedimentation rates were relatively low throughout the late Eocene-Quaternary for a setting close to land (6.9-1.5 cm/k.y.). The succession of sediment, climatic, and biotic changes recorded at Site 1168 was interpreted to reflect the three major steps in Cenozoic climate state, namely, "Greenhouse" in the late Eocene, "Doubthouse" of intermediate mode in the Oligocene-early Miocene, and "Icehouse" since the middle Miocene (Shipboard Scientific Party, 2001a). Relatively rapid changes mark the boundaries at the Eocene-Oligocene transition and during the middle Miocene at ~14 Ma. The most conspicuous change in the sediment and biotic sequence occurred during the transition from the latest Eocene to the early Oligocene, with an apparent reduction in sedimentation rates, deposition of glauconite sands, and a possible hiatus in the earliest Oligocene (Stickley et al., this volume). This transition is seen to reflect a transient event associated with temporarily increased bottom water activity in the basin (Shipboard Scientific Party, 2001a). The timing of this episode is apparently consistent with the hypothesis linking the critical deepening of the Tasmanian Gateway to major cooling of Antarctica and associated cryospheric development (see also Stickley et al., submitted [N1]). However, these links are as yet poorly understood (see discussion in Huber et al., submitted [N2]). For further information on the general geologic and oceanographic setting of Site 1168, see reviews in Shipboard Scientific Party (2001a, 2001b).
Organic-walled microfossils were extracted for analysis using standard palynological processing techniques at the Laboratory of Palaeobotany and Palynology at Utrecht University. From the core samples, ~5 cm3 of wet sediment was oven-dried at 60°C and weighed (8-14 g). Processing involved an initial treatment in hydrochloric acid (10%) to dissolve carbonates, followed by a treatment of hydrofluoric acid (38%) to dissolve silicates. After each acid step, samples were washed two times by decanting after 24 hr settling and filling up with distilled water. The hydrofluoric step included 2 hr shaking at ~250 rpm and adding 30% hydrochloric acid to remove fluoride gels. Then, samples were repeatedly washed in distilled water and finally sieved through a 15-µm nylon mesh sieve (10 µm nylon mesh sieve for Quaternary samples). To break up clumps of residue, the sample was placed in an ultrasonic bath for a maximum of 5 min after the first sieving. The residue remaining on the sieve was transferred to a glass tube. The tubes were centrifuged for 5 min at 2000 rpm and the excess amount of water was removed. For slide preparation, residues were transferred to vials and glycerin water was added. The residue was homogenized, no coloring was added, a droplet of each residue was mounted on a slide adding glycerin jelly, and the mixture was stirred and sealed with nail varnish. Two slides per sample were prepared.
Where possible, slides were initially counted to 200 palynomorphs, followed by the counting of 200 or more dinocysts. When dealing with low yields, counting was stopped after two slides at this stage (see Table T1). Dinocysts were counted at species level, whereas other palynomorphs were counted in broad categories, namely, bisaccate pollen, other pollen, spores, inner linings of foraminifers (if >3 chambers), remains of prasinophyte or chlorophyte algae such as Cymatiosphaera and Tasmanites spp., remains of Copepod eggs, and acritarchs. Here, of these other palynomorphs, only the calculated terrestrial percentage is presented to provide a general characterization (Table T1; Fig. F2). Aquatic palynomorphs are usually dominated by dinocysts. The lower Miocene interval is, however, characterized by massive influxes of small skolochorate acritarchs (palynomorphs of unknown affinity); this is an exceptional phenomenon. These microfossils occur in up to two orders of magnitude larger concentrations than dinocysts. Samples characterized by such huge influxes of acritarchs are marked in Table T1, but numbers were kept separate from the general palynomorph count as they obscure trends in relative terrestrial palynomorph abundance, for example.
The postcruise studies are here supplemented by the onboard studies performed on core catcher material. Essentially, shipboard processing followed the steps as described above, using a 20-µm stainless steel sieve (leading to the potential loss of small palynomorphs), and equipment was not as sophisticated as common modern laboratory setups. Results from these shipboard samples should be taken as rough estimations.
Cyst taxonomy follows that cited in Williams et al. (1998) and Rochon et al. (1999). A species list, including remarks on new taxa, is presented in the "Appendix". For the purpose of the present study, which only provides a broad overview of the dinocyst distribution and general palynological contents, emphasis is placed on potential age-diagnostic taxa. Other species are placed in generic groups (see the "Appendix"). Future studies will consider dinocyst distribution of rare species, besides other aspects, in more detail. Slides are stored in the collection of the Laboratory of Palaeobotany and Palynology, Utrecht University.
We adopt the postcruise age model as presented in Stickley et al. (this volume) for Hole 1168A. Ages (in mega-annum [Ma]) are indicated in Table T1 where relevant; for more detailed information see Stickley et al. (this volume). As an indication, the Pliocene/Pleistocene boundary occurs at ~16 mbsf, the early/late Pliocene boundary at ~46 mbsf, the Miocene/Pliocene boundary at ~92 mbsf, the middle/late Miocene boundary at ~190 mbsf, the early/middle Miocene boundary at ~265 mbsf, the Oligocene/Miocene boundary at ~420 mbsf, the early/late Oligocene boundary at ~580 mbsf, the Eocene/Oligocene boundary (sensu Global Stratotype Section and Point [GSSP]) at ~745 mbsf, and the middle/late Eocene boundary close to the bottom of the hole (~880 mbsf). Using this age model, sedimentation rates varied from ~3.5 cm/k.y. in the Eocene to ~1.5 cm/k.y. during most of the Neogene (Stickley et al., this volume).