Twelve papers appearing in this volume add significant knowledge to the Cenozoic paleoenvironmental development of the region. These contributions are briefly summarized as follows.
Stickley et al. (this volume) summarize the Late Cretaceous to Quaternary biostratigraphy and calibrate this with magnetostratigraphy. Their age models for Sites 1168, 1170, 1171, and 1172 (see Fig. F5) integrate information from calcareous, siliceous, and organic walled microfossils. These data provide the necessary chronologic foundation upon which all other research papers from Leg 189 depend. The study is a unique synthesis of latest Cretaceous to Quaternary biostratigraphy in the Australian-Antarctic region, using all key microfossil groups.
Robert (this volume) presents a data report on bulk and clay mineral assemblages for the entire sequences at all sites except Site 1169. He provides detailed data tables and informative graphs and background information for Robert (in press). Differences in clay mineral assemblages are related to source material, regional tectonics, weathering, and erosion. At the eastern sites (1170–1172) a threefold split in bulk sediment mineralogy matches lithologic changes: lower upper Eocene and older siliciclastics (terrigenous minerals), uppermost Eocene–Oligocene transition (terrigenous minerals plus some biogenic carbonate), and Oligocene and younger carbonates (biogenic carbonate minerals). At Site 1168 the terrigenous–carbonate transition is gradual, with terrigenous minerals common until the lower middle Miocene. The clay mineral assemblages do not differ from east to west as much as the bulk mineralogy. Smectite is mostly dominant, with variable subordinate proportions of kaolinite and illite. Chlorite is commonly present at Sites 1170–1172.
Latimer and Filipelli (this volume) provide a data report on Eocene to present sediment geochemical results from Site 1171. Fe, Al, and Ti concentrations and elemental ratios (carbonate free) were measured to identify changes in metal sources and terrigenous inputs. Export production was studied using P and Ba concentrations and P/metal and Ba/metal; higher values represent higher production. There are major changes at ~260–290 mbsf (Eocene–Oligocene transition), where siliciclastic sediments grade upward into pelagic carbonate sediments. P/Ti and Ba/Ti ratios indicate large export production increases, the ratios changing from negligible in the Eocene to ~6–10 g/g in the Oligocene. The ratios declined gradually to ~4 g/g in the Pliocene–Pleistocene.
Williams et al. (this volume) compare Southern Ocean and global dinoflagellate cyst index events for the Late Cretaceous to Neogene. They use Leg 189 sites for much of the Southern Ocean control, and these sites have the benefit of detailed independent age control, primarily from magnetostratigraphy and, to some extent, from planktonic foraminifers and calcareous nannofossils. Williams et al. carefully document stratigraphic ranges of the dinocysts with abundant line drawings of taxa and photomicrographs provided to assist with identification, a useful resource for the international community of dinocyst workers.
Brinkhuis, Sengers, et al. (this volume) describe latest Cretaceous to earliest Oligocene (and Quaternary) dinoflagellate cysts from Site 1172 on the East Tasman Plateau, providing a standard reference for dinocyst biostratigraphy for these latitudes during the latest Cretaceous through the Oligocene. The Maastrichtian to earliest Oligocene record is well represented, with the exception of much of the early and some of the late Paleocene. Dinocyst species are largely endemic and relatively cool water, representing the "Transantarctic Flora," or are bipolar types. Until the early late Eocene, the assemblages are indicative of shallow-marine to restricted-marine, prodeltaic conditions. By middle late Eocene times, slow glauconitic sedimentation became established, reflecting the deepening of the Tasmanian Gateway. An associated notable turnover in dinocyst associations reflects a change from marginal marine to more offshore conditions. Organic microfossils are virtually absent in the Oligocene and Neogene pelagic carbonates.
Brinkhuis, Munsterman, et al. (this volume) provide an important overview paper on late Eocene, Oligocene, Miocene, and Quaternary dinoflagellate cyst distributions at Site 1168 west of Tasmania and illustrate the main trends in palynomorph distribution. The dinocyst species are largely cosmopolitan with some low-latitude taxa and, unlike those at Site 1172 to the southeast, the assemblages do not contain endemic Eocene Antarctic taxa. The general palynomorph distributions suggest relatively warm waters, an initially restricted shallow-marine setting, and deepening and initiation of open-ocean conditions in the Oligocene.
Sluijs et al. (this volume) describe dinoflagellate cysts from the Eocene–Oligocene transition, particularly for Site 1172 on the East Tasman Plateau and Sites 1170–1171 on the South Tasman Rise, and compare the results with broader shipboard information from Site 1168 west of Tasmania. At Sites 1170–1172, three distinctive dinocyst assemblages indicate relatively rapid stepwise environmental changes, from a prodeltaic to a deeper marine pelagic setting. The Antarctic endemic assemblage was replaced by a more cosmopolitan offshore assemblage at ~35.5 Ma and by an even further offshore assemblage at ~34 Ma.
Wei et al. (this volume), in a brief data report on the Paleogene calcareous nannofossil biostratigraphy of Leg 189, list the distribution of nannofossils at the various sites and summarize the occurrence of nannofossil datums. The nannofossil assemblages are particularly important in establishing the biostratigraphy of Oligocene carbonate sequences. They also provide sporadic but valuable ages and environmental information for the pre-Oligocene siliciclastic sequences.
Pfuhl and McCave (this volume) built integrated age models for the early Oligocene to early Miocene (30–14 Ma) at four sites, comparing biostratigraphy, magnetostratigraphy, stable isotope records, carbonate content, and weight percent sand. They show that the Marshall Paraconformity (named in New Zealand) forms a hiatus (~33–30 Ma) at the eastern sites but is essentially absent at Site 1168. At the two easternmost sites (1171 and 1172), the Oligocene/Miocene boundary is marked by a condensed section or hiatus (~24–23 Ma). There is a problematic mismatch of the Mi-1 event (~24 Ma) at Sites 1168 and 1170.
Ennyu and Arthur (this volume) provide a data report on oxygen and carbon stable isotope records of Miocene planktonic and benthic foraminifers and fine-fraction carbonate from Sites 1170 and 1172, as background for interpretations provided in Ennyu and Arthur (in press).
McGonigal and Wei (this volume) provide a data report on Miocene calcareous nannofossil biostratigraphy containing species range charts, a tabulation of key biohorizons, a summary of nannofossil zones and datums, and plates of photomicrographs. Although diversity and biostratigraphic resolution were greatest at Site 1168, a solid integrated biostratigraphy was constructed at all sites by incorporating the results from other microfossil groups and magnetostratigraphy.
Stant et al. (this volume) report on the Quaternary nannofossil biostratigraphy of four sites: two north and two south of the present-day Subtropical Front. Their study indicates that movement of the front in the Quaternary and late Pliocene influenced the distribution of warmth-loving Discoaster and large Gephyrocapsa species. In addition, discoasters survived longer (until 1.95 Ma) east of Tasmania at Site 1172 than west of Tasmania (until 2.51 Ma), suggesting that the East Australian Current warmed the eastern waters. An early Pleistocene hiatus encompasses the entire Helicosphaera sellii Zone, as it does at many other DSDP and ODP sites in the region.