Ocean Drilling Program (ODP) Site 1172 is located in a water depth of ~2620 m on the flat western side of the East Tasman Plateau (ETP), ~170 km southeast of Tasmania (Fig. F1). At 44°S, the site lies in cool subtropical waters just north of the Subtropical Front. During the middle Eocene, however, the ETP was at ~65°S when its relatively fast northward movement (55 km/m.y.) with Australia commenced (Shipboard Scientific Party, 2001a). Drilling at Site 1172 penetrated some 766 m of uppermost Cretaceous-Quaternary sediments. Initial studies indicated that ~70 m of black shallow-marine mudstones of latest Cretaceous (Maastrichtian) age are overlain by ~335 m of Paleocene and Eocene brown, green, and gray shallow-marine mudstones and ~364 m of Oligocene and Neogene pelagic carbonates (Shipboard Scientific Party, 2001c). The pelagic carbonates reflect ever-increasing depths following relatively rapid latest Eocene-earliest Oligocene subsidence, while much of the Oligocene and lower Miocene section is thought to be missing because of current action. Underlying Paleogene and latest Cretaceous siliciclastics were deposited at shallow depths. The sedimentary record at Site 1172 thus has captured the tectonic evolution of the opening of the Tasmanian Seaway, its deepening, and the voyage northward from ~70°S to its present location at 44°S.
Shipboard palynological analysis indicated that well-preserved organic walled dinoflagellate cysts (dinocysts) and sporomorphs are present in the Quaternary interval. In contrast, it appeared that the remaining Neogene-lower Oligocene strata are virtually devoid of acid-resistant organic matter, whereas dinocysts are the dominant constituent of the rich Maastrichtian to earliest Oligocene palynological associations. Other microfossils are present in the Cenozoic and uppermost Cretaceous sequence at Site 1172 with the dominance of different groups changing with depositional environments. Calcareous groups are most prominent from the Oligocene upward, whereas siliceous and organic groups are most common below this level (see overview in Shipboard Scientific Party, 2001c). The basic architecture of the sedimentary succession of Site 1172 is similar to that of the other Leg 189 sites in recording three major phases of paleoenvironmental development, namely (1) Maastrichtian-early late Eocene deposition of shallow-water siliciclastic sediments during rifting between Antarctica and the South Tasman Rise (STR), (2) a transitional latest Eocene condensed interval with shallow-water glauconitic siliciclastic sediments giving way to deepwater pelagic carbonates representing the activation of bottom currents as the Tasmanian Gateway deepened during early drifting, and (3) earliest Oligocene-Quaternary deposition of pelagic carbonate sediments in increasingly deeper waters and more open-ocean conditions as the Southern Ocean developed and expanded with the northward flight of the ETP and the Australian continent (Shipboard Scientific Party, 2001a).
The primary objectives of coring and logging at Site 1172 were to:
For this purpose, a selection of samples from Holes 1172A and 1172D, covering the Maastrichtian-lowermost Oligocene, was palynologically analyzed. In addition, a selection of samples from the Quaternary interval was analyzed as well. Considering that the latest Cretaceous-Paleogene succession of Site 1172 has a confident magnetostratigraphy, calibrated against biotic events, great potential to tie dinocyst events to the geomagnetic polarity timescale (GPTS) and cyclostratigraphy (Röhl et al., submitted [N1]) is available here.
Shipboard analysis indicated that most of the Oligocene-Pliocene interval is barren of organic remains, and follow-up studies thus far have not further considered this interval. However, since these findings are only based on core catcher materials and onboard processing, further study should confirm this aspect. Here, we provide an overview of the dinocyst distribution from the Maastrichtian to lowermost Oligocene and Quaternary interval. Several new taxa have been recorded; some of them are informally characterized herein and others are placed in broad generic groups. Future work on this material will describe these taxa formally, and more details, also on other constituents of applied generic groupings, will be presented. Results of more detailed studies, including palynology, considering prominent boundaries at Site 1172 (e.g., Eocene/Oligocene, Paleocene/Eocene, and Cretaceous/Tertiary boundaries) are presented elsewhere (Sluijs et al., this volume; Stickley et al., submitted [N2]; Röhl et al., submitted [N1], [N3]; Schellenberg et al., submitted [N4]).