In this paper, we are principally concerned with providing overall trends emerging from the initial data set. For this purpose, trends in the relative abundance of terrestrial palynomorphs and oceanic (non-neritic) dinocysts are depicted in Figure F2. Species marked with (o) in Table T1 have been used to generate this curve, making use of previous studies focusing on global modern dinocyst distribution and empirical paleoenvironmental evidence from a wide variety of sources (e.g., Brinkhuis and Biffi, 1993; Brinkhuis, 1994; Stover et al., 1996).
The succession at Site 1168 was interpreted to reflect an initial shallow-water, nearshore, restricted marine setting with poor ventilation and siliciclastic sedimentation, low oxygenation, and high organic carbon deposition during the late Eocene (Shipboard Scientific Party, 2001a, 2001b). Site 1168 Eocene sediments are similar in nature to those at Cape Sorell (Boreham et al., 2002) and to those reported from DSDP Site 282 to the northwest, suggesting widespread late Eocene suboxic to anoxic conditions in the eastern Australo-Antarctic Gulf. Following a transitional phase during the Oligocene, in the Neogene these conditions had been replaced by deposition of carbonate ooze in a well-oxygenated open ocean on a passive margin at middle bathyal depths (Shipboard Scientific Party, 2001ab; Boreham et al., 2002). The curves of Figure F2 both confirm the broad trend of initial shallow-marine, nearly continental conditions evolving into an open oceanic environment. A marked acceleration of this process apparently occurred near the end of the early Miocene as indicated by a distinct step in the relative abundance of oceanic dinocysts (Fig. F2). Variations in both curves during the late Eocene-early Oligocene may be explained by the influence of third-order eustatic sea level changes, as further research will possibly show in more detail. A marginal marine deltaic setting during the late Eocene is consistent with the relatively poorly diversified nature of the dinocyst assemblages, with sporadic optima of peridinioid species such as Deflandrea phosphoritica and gonyaulacoid taxa as Cooksonidium capricornum, Operculodinium, and Spiniferites spp. (the latter when more open-marine, neritic conditions arrived) (cf. Brinkhuis, 1994; Stover et al., 1996). The dinocyst assemblage in this interval is very similar to those recorded elsewhere from ancient Eocene-Oligocene delta-front deposits (Brinkhuis et al., 1992; Brinkhuis and Biffi, 1993; Brinkhuis, 1994). The Oligocene assemblages are characterized by a slight increase in diversity, with increasingly consistent occurrences of more open-marine neritic to offshore taxa such as T. pelagica, Cleistosphaeridium, and Hystrichokolpoma spp., besides ever-increasing numbers of typical oceanic taxa such as Nematosphaeropsis and Impagidinium spp. (Fig. F2). A general long term (post-Eocene) oligotrophic nature of the surface waters influencing Site 1168 is suggested from the low abundance of (proto) peridinioid, presumably heterotrophic species.
An important general aspect in the dinocyst assemblages is the near absence of Antarctic endemic (Transantarctic) species and the apparent influence of relatively warm waters throughout the succession at Site 1168. As explained above, the dinocyst assemblages are to a high degree comparable with those reported from low latitudes, although cosmopolitan taxa (e.g., Spiniferites spp., Operculodinium spp., and Nematosphaeropsis spp.) are common as well. This aspect suggests a long-term overall warm to warm-temperate nature of the surface waters influencing Site 1168. The Tethyan index taxa display a rather patchy distribution pattern, suggesting that these horizons indicate maximum surface water warmth and/or maximum influence of water masses originating from low latitudes, possibly reflecting transportation. Conversely, already in Eocene and Oligocene times, occasional influence of colder (cold temperate) water masses is apparent as well, judging from the distribution patterns of cool-temperate species such as Gelatia inflata and Impagidinium velorum, besides some of the Transantarctic Flora species discussed above. Overall, the assemblages may thus be described as being warm temperate in nature.
Specifically, the late Eocene assemblages are characterized by the concomitant presence of typical lower-latitude and cosmopolitan taxa, suggesting subtropical to warm-temperate conditions. This aspect matches reports on the nature of the Eocene and early Oligocene vegetation in the region, which suggests that air temperatures were subtropical to warm temperate and always above freezing (Greenwood and Wing, 1995). Indeed, the inference of warm-temperate surface water conditions also matches earlier reports based on other microfossil groups and stable isotope studies.
On the basis of stable isotope studies (e.g., Kamp et al.,1990; Buening et al., 1998), inferred surface water temperatures ranged from ~12° to 20°C for the region during the late Eocene. Calcareous microfossil studies in the region indicate similar temperatures, indicating a long-term influence of a proto-Leeuwin Current (e.g., McGowran et al., 1997; Li et al., 2000, 2003; Nelson and Cooke, 2001). Li et al. (2003), studying foraminifers from ODP Leg 182 drill sites, specifically state (p. 1) "...The southern temperate assemblage hosted several subtropical species in the middle-late Eocene and Oligocene as immigrants probably transported by a warm-water system similar to the present-day Leeuwin Current..." This interpretation perfectly describes the dinocyst signal at Site 1168 as well.
In the Neogene, assemblages are also marked by an abundance of warmer-water species (in this case many Impagidinium species, indicating relatively warm, oligotrophic oceanic surface water conditions throughout) (cf. Rochon et al., 1999). In the Quaternary interval, a few specimens of the bipolar (cold) species I. pallidum are recorded as well. This aspect indicates the influence, albeit limited, of colder surface water masses in this interval or deep transport by possibly colder underlying waters.