Ocean Drilling Program (ODP) Site 1168 is located in middle bathyal water depths (2463 m) on the slope of the western margin of Tasmania (Fig. F1). Hole 1168A penetrated marine rift to open-margin sediments deposited from the early late Eocene onward as Australia moved northward from Antarctica (Shipboard Scientific Party, 2001ab). Initially, in the Eocene, the site was at the far eastern end of the restricted Australo-Antarctic Gulf and separated from the Pacific Ocean by the Tasmanian Promontory-South Tasman Rise. Plate movements and related margin subsidence led to its Neogene location in open water facing a broad Southern Ocean to the west.
Microfossils belonging to seven major groups were recovered from the sedimentary succession at Site 1168. The combined shipboard results indicate that the upper Eocene-Quaternary succession is essentially complete. Of the siliceous groups, diatoms are generally rare and sporadic, whereas radiolarians are generally rare but occasionally abundant. Calcareous microfossils (foraminifers and nannofossils) are generally abundant down to the basal Oligocene. Benthic foraminifers are present throughout the entire sequence, with the upper Eocene showing low abundances and diversity of mainly agglutinating species. Onboard studies also indicated the presence and local abundance of organic-walled dinoflagellate cysts (dinocysts) in the succession of Hole 1168A. Dinocysts are rare in the middle Miocene, whereas sporomorphs are reported to dominate the palynomorph assemblages in samples from the lower part of Hole 1168A assigned to the late Eocene (Shipboard Scientific Party, 2001b). Rather unique to this site, compared to other ODP Leg 189 sites or other locations in the Southern Ocean, is the reasonably consistent occurrence of dinocysts throughout the Oligocene and Neogene deposits (Shipboard Scientific Party, 2001a).
So far about two to three samples per core (average spacing = ~4 m) from Hole 1168A were subjected to palynological analysis. Besides dinocysts, broad categories of other palynomorphs were quantified. Here, we aim to provide an overview of the dinocyst distribution from the upper Eocene-Quaternary interval and to illustrate main trends in palynomorph distribution. Several new dinocyst taxa have been recorded; some of them are informally characterized herein, others are placed in broad generic groups. Future work on this material will describe these taxa formally and more details on other constituents of applied generic groupings will be presented therein. Because only very few previous dinocyst studies are available, for age assessment of first occurrences (FO) and last occurrences (LO) of taxa, we principally rely on the age model provided for Site 1168 constructed by other means (Stickley et al., this volume). Comparison of ranges may only be performed on the basis of Northern Hemisphere records and are herein only discussed for a few species, where appropriate.