Dinocyst distribution, relative abundance of terrestrial palynomorphs, samples with massive influx of acritarchs, as well as percentages of non-neritic (oceanic) dinocysts (see explanation below) are depicted in Table T1. A summary of selected potentially stratigraphically useful dinocyst events and derived ages is given in Table T2. Plots of percent terrestrial palynomorphs and percent oceanic dinocysts vs. depth and age are given in Figure F2.
Recovery of palynomorphs is quite variable. Dinocysts are in most cases the most prominent palynomorphs in the uppermost Eocene-lower Miocene and in the Pliocene and Quaternary. Sporomorphs dominate the upper Eocene and are frequent in the overlying palynological associations (Fig. F2), as are the organic linings of foraminifers. Sporadic occurrences of representatives of the chlorophyte Tasmanites, as well as other prasinophytes, have been recorded in some samples (not shown). Massive influxes of small skolochorate acritarchs of unknown affinity (Pl. P1, figs. 140-151) occur between ~387 and 210 mbsf (upper lower-lower middle Miocene). Pulses of up to 1000 acritarchs vs. 1 dinocyst predominantly occur between 385 and 340 mbsf. The dinocyst (and palynological) record becomes patchy in the middle Miocene-basal Pleistocene interval. Probably, the low sedimentation rates and related prolonged exposure to oxic conditions hampered significant accumulation of organic matter, including organic-walled dinocysts.
Despite many attempts, only few studies of Oligocene-Neogene dinocysts are available from the circum-Antarctic domain; representatives of this fossil group have been found only sporadically (see overviews in Hannah et al., 1998; Wrenn et al., 1998; McMinn et al., 2001; Harland and Pudsey, 2002). This contrasts markedly the situation in the older Paleogene, where many studies have reported rich dinocyst associations around Antarctica (e.g., Goodman and Ford, 1983; Wilson, 1985, 1988; Wrenn and Hart, 1988; Mohr, 1990; Mao and Mohr, 1995; Crouch and Hollis, 1996; Truswell, 1997; Hannah, 1997a, 1997b; Hannah and Raine, 1997, Brinkhuis et al., this volume; Sluijs et al., this volume, for overviews). Only recently a first ever quasi-continuous Southern Ocean Oligocene-early Miocene dinocyst succession was documented from the Ross Sea continental shelf (Cape Roberts Project, see Hannah et al., 2000, and discussion in Brinkhuis et al., this volume). In effect, McMinn (1995) noted the absence of Neogene dinocysts and postulated that the loss of shelves (due to glaciation) from the Antarctic continent from the basal Oligocene onward contributed to this local extinction of the cyst-producing dinoflagellates. Rather, as also suggested by Wrenn et al. (1998), the organic wall of the dinocysts is not resistant to the oxygen-rich waters in the Antarctic domain and/or winnowing at depth and/or low sedimentation rates precludes preservation of these microfossils (e.g., Zonneveld et al., 1997, 2001; Versteegh and Zonneveld, 2002; Hopkins and McCarthy, 2002). Southern Ocean dinocyst assemblages should be present when preservation requirements are met. The studies by, for example, Hannah et al. (2000) on the Ross shelf or McMinn et al. (2001) analyzing Pliocene dinocysts and diatoms from Deep Sea Drilling Project (DSDP) Site 594, Chatham Rise, illustrate this aspect. Moreover, McMinn and Wells (1997) already demonstrated the potential of dinocyst analysis for paleoenvironmental reconstructions in the Quaternary in the region using piston-cored materials from locations close to Site 1168. The relative abundance of dinocysts in the Oligocene-Neogene of Site 1168 may therefore be taken to indicate that water mass, bottom conditions, and sedimentation rates were suitable for preservation of organic material.
Dinocyst species throughout Hole 1168A are largely cosmopolitan and rather long ranging, with important contributions of typical low-latitude taxa. Dinocyst stratigraphic distribution broadly matches that known from the Northern Hemisphere and equatorial regions, although significant differences are noted (see below). Selected potentially biochronostratigraphically useful events are summarized in Table T2. Unfortunately, the distribution of dinocysts in the middle-upper Miocene is rather patchy due to reasons discussed above. This hampers detailed cross-hemisphere comparisons. For example, the ranges of species stratigraphically important in Northern Hemisphere Neogene deposits such as Achomosphaera andalousiensis, Cerebrocysta poulsenii, Edwardsiella sexispinosum, and Labyrinthodinium truncatum, broadly match those recorded here, but not in detail, probably due to poor preservation/oxidation. The Eocene-Oligocene to perhaps lower Miocene interval has more potential for detailed comparisons (see below). Consistent with earlier studies based on other microfossil groups suggesting that a relatively warm current akin to the Leeuwin Current (or "proto-Leeuwin Current") dominated this region for the last ~40 m.y. (e.g., Li et al., 2003; Huber et al., submitted [N2]), the suite of events recorded in Hole 1168A has much in common with those known from southern European (Tethyan) successions (like those reported by, e.g., Biffi and Manum, 1988; Brinkhuis et al., 1992; Brinkhuis and Biffi, 1993; Wilpshaar et al., 1996). Conspicuously, species belonging to the "Transantarctic Flora" (cf. Wrenn and Beckmann, 1982) are virtually absent. Only very few specimens of species belonging to this endemic flora are recorded at Site 1168 (e.g., Deflandrea antarctica, Octodinium askiniae, and Enneadocysta partridgei). Several yet undescribed species were recorded (e.g., new species of Cerebrocysta, Hystrichokolpoma, Eocladopyxis, and Cannosphaeropsis). They will be treated in more detail elsewhere.
Although the latest middle-late Eocene dinocyst record of Hole 1168A is somewhat patchy, probably due to the extremely shallow marine setting, the species composition broadly matches that described from the southeastern Australian surface section at the Browns Creek locality (Cookson and Eisenack, 1965; Stover, 1975). Ranges of, for example, Schematophora speciosa, Aireiana verrucosa, Hemiplacophora semilunifera, and Stoveracysta ornata appear useful for regional and even broad global correlation. Many of the Browns Creek late Eocene dinocysts have been recorded from locations around the world, but notably in central and northern Italy, including the Priabonian-type section (Brinkhuis and Biffi, 1993; Brinkhuis, 1994). It appears that these index species have slightly earlier range tops in this region than in the Tethys. This may be related to the progressive cooling during the late Eocene and/or the warm-temperate nature of the surface waters (see discussion below). The dinocyst distribution across the Eocene/Oligocene boundary, also from other Leg 189 sites, is discussed in more detail in Sluijs et al. (this volume).
It is likely that older Paleogene and Cretaceous deposits underlie the upper Eocene at Site 1168, not recovered during Leg 189 drilling. Studies of the nearby borehole at Cape Sorell indicate the presence of at least ~2400 m of Campanian/Maastrichtian-middle Eocene sediments in the immediate surroundings of Site 1168 (Boreham et al., 2002). Palynological studies (MacPhail in Boreham et al., 2002) indicate that the signature of these deposits is very similar to those recovered at Site 1168, with endemic species being relatively rare. This contrasts with results from dredge samples taken slightly farther to the south, along the South Tasman Rise (Truswell, 1997). Samples assigned to the middle Eocene there are characterized by the distinct presence of the Transantarctic Flora (Truswell, 1997). It is therefore apparent that completely different surface waters influenced sites more to the south from Site 1168 and Cape Sorell. Onboard results from Sites 1170 and 1171, also showing high abundances of the Transantarctic Flora in the Eocene, on the South Tasman Rise confirm this aspect (Shipboard Scientific Party, 2001c, 2001d; Brinkhuis et al.; Sluijs et al., both this volume).
Relatively poorly diversified assemblages characterize the Oligocene succession at Site 1168 with long-ranging cosmopolitan representatives of Spiniferites, Operculodinium, Hystrichokolpoma, and Cleistosphaeridium being common to frequent. Thalassiphora pelagica and Apteodinium australiense may be abundant in certain intervals. The near absence of Deflandrea spp. or of any (proto) peridinioid (probably heterotrophic) dinocysts is remarkable. Yet, other dinocysts are present in the background, albeit with a scattered distribution. The succession of events in this background pattern in the Oligocene interval shows remarkable resemblance to the succession of central Italy as summarized in Wilpshaar et al. (1996). Tethyan index species such as Areoligera? semicirculata, Wetzeliella gochtii, Hystrichokolpoma sp. cf. Homotryblium oceanicum, Hystrichokolpoma pusilla, Chiropteridium spp., Distatodinium biffii, and Ectosphaeropsis burdigalensis have virtually the same stratigraphic succession here as they display in Italy. They do, unfortunately, have a rather patchy distribution pattern at Site 1168, whereas they occur more consistently in Italy. For example, the FO of D. biffii matches its reported FO in Italy, following the current age model; its LO, however, occurs earlier at Site 1168. This may be due to the scarcity of this index fossil and the current rather large sample spacing. The scattered occurrences of Hystrichokolpoma sp. cf. H. oceanicum, H. pusilla, and Chiropteridium spp. basically fall within their ranges in Italy, but the pattern at Site 1168 is inconsistent so far. The FO of E. burdigalensis, an index event for recognition of the Oligocene/Miocene (O/M) boundary in Italy (Brinkhuis et al., 1992), apparently occurs much earlier at Site 1168, if the current age model is accepted. It thus appears that this species migrated from Southern Hemisphere locations to the Northern Hemisphere at or about O/M times. However, a recent study of Chattian deposits in Belgium reports the FO of E. burdigalensis to occur well below the O/M boundary as well (van Simaeys et al., in press). Combined evidence therefore suggests this form to be a temperate to warm-temperate species. The FO of E. burdigalensis is followed upsequence by the successive FOs of Membranilarnacia? picena and a form morphologically similar to Stoveracysta conerae (Stoveracysta cf. conerae) at Site 1168. This pattern is identical to the Italian lower Miocene succession, but this suite of events appears (much) earlier at Site 1168. Remarkably, the FO of D. biffii practically coincides with a single influx of Svalbardella spp. This conjunction of events mimics the situation in central Italy (Wilpshaar et al., 1996) and can even be traced to near the Rupelian/Chattian boundary in their type region (Van Simaeys et al., in press). In Italy, most recent information places these events at the base of Chron C9n (Prof. R. Coccioni, University of Urbino, pers. comm., 2003). The integrated magnetobiostratigraphic age model for Hole 1168A also indicates these events to be associated with the base of Chron C9n. Although international debate on the GSSP of the Rupelian/Chattian is ongoing, indications are that this episode will be selected to represent this important boundary in geological history. The aforementioned dinocyst events apparently have a widespread nature and may well be associated with a pronounced episode of global cooling (possibly oxygen isotope [Oi] event Oi2b; e.g., Miller et al., 1998) that affected surface waters and circulation worldwide. The O/M transition around ~410 mbsf is characterized by a marked influx of A. australiense and a new species of Eocladopyxis (Table T1).
The distribution of dinocysts in the middle-upper Miocene is rather patchy due to reasons discussed above. The lower Miocene, however, has reasonable recovery and basically shows the same basic pattern as the Oligocene: relatively poorly diversified assemblages, with long-ranging cosmopolitan representatives of Spiniferites and Operculodinium being common to frequent. Cerebrocysta spp. and Reticulatosphaera actinocoronata may be abundant in certain intervals. Typical oceanic (non-neritic) taxa such as Nematosphaeropsis and Impagidinium spp. markedly increase in abundance from the lower Miocene onward (Fig. F2). Pentadinium laticinctum has an acme near the top of the lower Miocene. Typical background taxa are Invertocysta spp. and E. sexispinosum. In the younger Miocene, where samples yield reasonably preserved dinocysts again, these trends continue, while potential index taxa, also relevant for cross-hemisphere comparison, such as A. andalousiensis, C. poulsenii, Mendicodinium sp. A of Wrenn and Kokinos, 1986, and L. truncatum are sporadically present. Several taxa have apparent range tops in the middle and upper Miocene interval but, again, the patchy record precludes any conclusions at this stage. As for the Oligocene, the near absence of (proto) peridinioid dinocysts is noteworthy. This group may reach high abundances in Neogene sequences around the world and is important for stratigraphic and environmental considerations (also discussed below). The virtual absence of cysts of Protoperidinium spp. may be related to poor preservation of organic materials in general or to the prevalence of oligotrophic water masses.
As noted above, notably the lower Miocene interval is marked by massive influxes of small skolochorate acritarchs. High magnification studies using scanning electron microscopy (SEM) (see Pl. P1, figs. 140-151) show that some of these appear to have angular openings similar to archaeopyles of dinoflagellate cysts. Although they probably represent a cyst stage of an unknown group of algae, further interpretation of this signal is not possible at this stage.
The Pliocene-Quaternary record is more consistent than the underlying Miocene interval, possibly due to changing oceanographic and depositional settings and/or sedimentation rates. Trends already apparent in the Miocene continued during the Pliocene to Quaternary (viz., ever-increasing abundances of typical oceanic species such as Nematosphaeropsis and Impagidinium spp.). The Pliocene interval is primarily marked by an influx of Operculodinium echigoense sensu McMinn (1992, 1993). This author recorded optima of this species at Sites 815 and 817 (Northeastern Australian margin) in the Pliocene and Pleistocene. This apparently tropical species has its optimum between 95 and 65 mbsf in Hole 1168A. Protoperidinioid species such as Brigantedinium spp. and Algidasphaeridum spp. begin to appear more consistently in the younger Pliocene. This and the overlying youngest interval of Hole 1168A are characterized by fluctuating abundances of the warm-water species Impagidinium aculeatum, Impagidinium paradoxum, Impagidinium patulum, and cosmopolitan Nematosphaeropsis spp. (cf. Rochon et al., 1999). Occasionally, the cold-water species Impagidinium pallidum is present as well. Similar assemblages were recovered from nearby sites (McMinn and Wells, 1997), although these authors did not report the presence of, for example, Algidasphaeridium spp. or Pentapharsodinium dalei.