Hole 1172A was piston cored to 522.6 meters below sea floor (mbsf) with 92.6% recovery. Hole 1172D was rotary cored from 344 to 373 mbsf, washed to 497 mbsf, and rotary cored to 766 mbsf with 80% recovery. Hole 1172D penetrated ~70 m of black shallow-marine mudstones of latest Cretaceous (Maastrichtian) age (to 766 mbsf). This sequence is overlain by ~335 m of Paleocene and Eocene brown, green, and gray shallow-marine mudstones, partly recovered in Hole 1172D (from 497 to 766 msbf) and down (and partly overlapping) to 522 mbsf in Hole 1172A. The lithostratigraphic sequence has been divided into four units, with three subunits in Unit I and two subunits in Units III and IV. For details, see the Leg 189 Initial Reports volume (Exon, Kennett, Malone, et al., 2001; Shipboard Scientific Party, 2001a, 2001b). The most remarkable lithologic change occurs at ~360 mbsf, within lithostratigraphic Unit II. This unit (355.8-361.12 mbsf) is a relatively thin uppermost Eocene-Oligocene (E-O) transitional unit. The sediments are mainly characterized by increased glauconite content and consist of variations of greenish gray glauconite-bearing silty diatomaceous claystone and dark greenish gray glauconitic diatomaceous clayey siltstone. This transition was considered to represent a condensed section or a hiatus. Carbonate content decreases from 69 wt% at the top to 0.3 wt% at the base (Shipboard Scientific Party, 2001c). Postcruise studies indicated the Cretaceous/Tertiary boundary (KTB) occurs at ~696 mbsf, marked by a distinct hardground. At this level, homogenous black mud to siltstones change over into more glauconite-rich gray to black sand and siltstones (see review in Shipboard Scientific Party, 2001c).
Reconstructed sedimentation rates at Site 1172 represent three distinct phases. In contrast to other Leg 189 sites, sedimentation rates were relatively low (between 2.6 and 1.04 cm/k.y.) in the Maastrichtian-uppermost Eocene. From the uppermost Eocene-middle Miocene (15 Ma), sedimentation rates decreased (0.16-3.2 cm/k.y.) and increased thereafter until the present day (see "Age Model"). These three basic intervals coincide with the succession in global climate change from the so-called "Greenhouse," via "Doubthouse," to "Icehouse" states. Site 1172, like Site 1168, appears to have been strategically located to record these overall shifts in global climate associated with development of the Antarctic cryosphere (Shipboard Scientific Party, 2001a). The most conspicuous change in the sediment and biotic sequence occurred during the transition from the latest Eocene to the earliest Oligocene, with conspicuous reduction in sedimentation rates and deposition of glauconite sands. Like at other Leg 189 sites, this transition reflects a transient event associated with temporarily increased bottom water activity in the basin. The timing of this episode is consistent with the hypothesis linking the deepening of the Tasmanian Gateway, major cooling of Antarctica, and associated cryospheric development (see also Stickley et al., submitted [N2]). However, these links are—as yet—poorly understood (see discussion in Huber et al., submitted [N5]). Moreover, the Oligocene-Quaternary sedimentary succession at Site 1172 was also interpreted to reflect an increase in ventilation (i.e., leading to a, at best, patchy Neogene palynological record). Like the other sites drilled during Leg 189, increased ventilation resulted from a fundamental change in paleogeography and oceanic circulation associated with increasing dispersal of the southern continents and the opening and/or deepening of the ocean basins at high latitudes in the Southern Hemisphere. For further information on the general geologic and oceanographic setting of Site 1172, see Shipboard Scientific Party (2001c).
On average, two to three samples per core (average spacing = ~3-4 m) from Holes 1172A and 1172D were palynologically analyzed (Tables T1, T2, T3). In certain intervals (Quaternary, Eocene/Oligocene, and Cretaceous/Tertiary), samples are more closely spaced (Tables T1, T2, T3). Results from onboard studies using core catcher samples have been integrated here with this first follow-up study.
Organic walled microfossils were extracted for analysis using standard palynological processing techniques at the Palynological Laboratory at the University of Utrecht.
From the core samples, ~15 g of wet sediment was collected, 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 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 with glycerin jelly, and the mixture was stirred and sealed with nail varnish. Two to four slides per sample were prepared.
Where possible, slides were initially counted to up to 200 or more dinocysts, while also counting associated other palynomorphs. When dealing with low yields of dinocysts, counting was stopped after two slides were examined (see Tables T1, T2, T3). Dinocysts were counted at species level, while other palynomorphs were counted in broad categories (namely, bisaccate pollen, other pollen spores, spores, inner linings of foraminifers [if more than three chambers], prasinophyte algae like Cymatiosphaera and Tasmanites spp., remains of Copepod eggs, and acritarchs).
The postcruise studies are here supplemented by the onboard studies performed on core catcher material. Essentially, shipboard processing followed the steps as described above but used a 20-µm stainless steel sieve (i.e., 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, only providing an 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 Tables T1, T2, T3). Future studies will consider dinocyst distribution of rare species, and so on, besides other aspects, in more detail.
We adopt the postcruise age model as presented in Stickley et al. (this volume) for Holes 1172A and 1172D. Ages (in Ma) are indicated in Tables T1, T2, T3, and T4 and in Figure F2 where relevant; for more detailed information see Stickley et al. (this volume). As an indication, the Pliocene/Pleistocene boundary occurs at ~21 mbsf, the early/late Pliocene boundary at ~49 mbsf, the Miocene/Pliocene boundary at ~87 mbsf, the middle/late Miocene boundary at ~238 mbsf, the early/middle Miocene boundary at ~311 mbsf, the Oligocene/Miocene boundary at ~335 mbsf, the early/late Oligocene boundary at ~354 mbsf, the Eocene/Oligocene boundary (sensu Global Stratotype Section and Point; GSSP) at ~356 mbsf, the middle/late Eocene boundary at ~377 mbsf, the early/middle Eocene boundary at ~550 mbsf, the Paleocene/Eocene boundary at ~620 mbsf, the middle/late Paleocene boundary at ~692 mbsf, and the KTB at ~696 mbsf. The bottom of Hole 1172D at 766 mbsf represents the earliest Maastrichtian.