Palynomorph and dinocyst distribution, as well as percentages of offshore (oceanic) dinocysts and terrestrial palynomorphs (see explanation below), are depicted in Tables T1, T2, T3. A summary of selected stratigraphically useful dinocyst events and derived ages is given in Table T4. Plots of percent terrestrial palynomorphs and percent offshore dinocysts vs. depth and age are given in Figure F2. Illustrations of taxa are shown in Plate P1.
Dinocysts are in most cases the most prominent palynomorphs throughout. Sporomorphs may dominate the Maastrichtian part of the succession and are frequent in the overlying palynological associations, notably in the upper Paleocene and lower Eocene (Fig. F2). Skolochorate acritarchs of various types, as well as remains of chlorophyte algae and foraminifer inner linings, occur in the background in the Paleogene and Quaternary associations (Tables T1, T2, T3).
Although many attempts to study Oligocene-Neogene dinocysts in the circum-Antarctic domain have been undertaken, they have only sporadically been found. Apparently, too often the organic wall of the dinocyst is not resistant to the oxygen-rich waters in the Antarctic domain and/or winnowing at depth, and low sedimentation rates preclude preservation of these microfossils (see discussion in Brinkhuis et al., this volume). Nevertheless, progress over the recent years has resulted in the documentation of an Antarctic Oligocene-earliest Miocene assemblage from the Ross Sea continental shelf (Cape Roberts Project; CRP) and several Miocene-Quaternary assemblages from the Weddell and Scotian Seas. (e.g., Wrenn et al., 1998; Hannah et al., 1998, 2000; McMinn et al., 2001; Harland and Pudsey, 1999, 2002; Harland et al., 1998, 1999).
In contrast, Late Cretaceous and Paleogene dinocysts from the broad Antarctic Realm or Southern Ocean are comparatively well known, notably from southern South America and from the James Ross and Seymour Islands, but also from southeastern Australia, New Zealand, from erratics along the Antarctic margin, the Ross Sea continental shelf (CRP), besides from several ocean drill sites (see overviews in, e.g., Haskell and Wilson, 1975; Askin, 1988a, 1988b; Wilson, 1985, 1988; Wrenn and Hart, 1988; papers in Duane et al., 1992; Pirrie et al., 1992; Mao and Mohr, 1995; Truswell, 1997; Hannah, 1997, Hannah et al., 2000; Levy and Harwood, 2000; Guerstein et al., 2002; Brinkhuis et al., this volume). Therefore, many studies have documented Circum-Antarctic/Southern Ocean Upper Cretaceous and Paleogene dinocyst distribution and taxonomy in great detail. Typically, however, meaningful chronostratigraphic calibration of dinocyst events is a classic problem due to the general absence of other age-indicative biota and/or magnetostratigraphy or other means of dating when dinocysts are encountered. Only recently, for the first time, integrated Oligocene-lowermost Miocene biomagnetostratigraphy, including dinocysts, was achieved on the basis of successions drilled during the Cape Roberts Project (Hannah et al., 1998, 2000).
Dinocyst species in the Maastrichtian-uppermost Eocene at Site 1172 are largely endemic (the so-called "Transantarctic Flora" sensu Wrenn and Beckmann, 1982) or bipolar; cosmopolitan taxa are present in varying, but on average, lower abundance as well. The lowermost Oligocene (a single productive sample only) and Quaternary interval has a stronger cosmopolitan to subtropical signature, with typical temperate to warm-water taxa being common to abundant, discussed further below.
The lower Paleogene dinocyst stratigraphic succession as well as its broad age range matches that known from New Zealand (e.g., Wilson, 1988, and references therein; Crouch, 2001). Maastrichtian-Paleocene associations are virtually identical to those known from Seymour Island (e.g., Askin, 1988a, 1988b; Elliot et al., 1994) and New Zealand (e.g., Wilson, 1978, 1984; Willumsen, 2000). During the middle Eocene, influence of the transantarctic dinocyst flora, constituted by species like Deflandrea antarctica, Octodinium askiniae, Enneadocysta partridgei, Vozzhennikovia spp., Spinidinium macmurdoense, and so on, increases and continues until the middle late Eocene. This aspect is quite different from the distribution patterns recorded at Site 1168 (Brinkhuis et al., this volume). The E-O transition is marked by a turnover from transantarctic dominated to associations dominated by new species of Brigantedinium and Deflandrea and the influx of Stoveracysta kakanuiensis. Lower Oligocene deposits are barren of palynomorphs, except for a single productive sample.
Several new taxa are recorded (e.g., new species of Batiacasphaera, Cerebrocysta, Cerodinium, Enneadocysta, Operculodinium, Dinopterygium, Impagidinium, Spiniferites, Vozzhennikovia, and Spinidinium), which will be treated in more detail elsewhere (see also "Appendix").
The Maastrichtian interval is characterized by relative abundant Manumiella spp., a typical situation for Antarctic dinocyst associations at this time (e.g., Wilson, 1978, 1984; Askin, 1988a, 1988b, 1999; Smith, 1992; Willumsen, 2000). No effort is taken here to further subdivide this group, but morphotypes (species) like Manumiella druggii, Manumiella seelandica, and Manumiella seymourensis are present, with the first being the most common. Alterbidinium (notably Alterbidinium acutulum), Diconodinium, Palaeocystodinium, and Cerodinium spp. further represent peridinioid cysts, including several new species. In general, peridinioid species (probably heterotrophic) are far more abundant than gonyaulacoid (autotrophic) cysts. In addition, new species of Operculodinium, Dinopterygium, and Spiniferites are prominent in these associations (Table T3). Of stratigraphic importance are the last occurrence (LO) of Odontochitina operculata near the base of the succession and the first occurrence (FO) of the Alisocysta reticulata group and Alisocysta circumtabulata, confirming a Maastrichtian age (cf. Askin, 1988a, 1988b; Willumsen, 2000). The KTB is here (at 696 mbsf in Hole 1172D), marked by the demise of Manumiella spp. and the massive influx of Palaeoperidinium pyrophorum, a feature also known from Seymour Island and New Zealand KTB successions (Askin, 1988a, 1988b; Willumsen, 2000). In the background, typical earliest Danian indicators like Trithyrodinium evittii and Senoniasphaera inornata have their FO (cf., e.g., Wilson, 1984; Strong et al., 1995; Brinkhuis et al., 1998). The massive turnover in the dinocyst assemblages, in conjunction with the recognized hardground at ~696 mbsf (near the top of Section 189-1172D-24R-5) point to a hiatus at the KTB. Occurrences of early Danian taxa (i.e., Trithyrodinium evittii and Senoniasphaera inornata) below the hardground are considered to result from downward bioturbation. The KTB hiatus apparently spans Chron C29R (Stickley et al., this volume; Schellenberg et al., submitted [N4]).
The Paleocene interval is marked by overall low-diversity, high-dominance episodes, (like, e.g., an acme of Glaphyrocysta spp.). In general, low-diversity associations prevail, with Cerodinium, Palaeocystodinium, Operculodinium, Hystrichosphaeridium, and Spiniferites spp. being common. Representatives of Alisocysta, Pyxidinopsis, and Alterbidinium consistently occur in the background. Palaeoperidinium pyrophorum, abundant just above the KTB (in Section 189-1172D-24R-5), is virtually absent in samples from Core 189-1172D-23R and younger. This species has a global LO near the base of the upper Paleocene (Thanetian) (e.g., Powell et al., 1995; Crouch, 2001; Williams et al., this volume), and this and other selected events (Table T4) suggest a late Paleocene age for the sequence until ~620 mbsf. This is confirmed by the FO of Deflandrea spp. near the top of this interval (cf. Crouch, 2001). Most of the lower and middle Paleocene (Danian-Seelandian) appears therefore to be missing or is extremely condensed.
Globally, the top of the Paleocene is marked by a massive influx of Apectodinium spp., especially during the Paleocene/Eocene Thermal Maximum or PETM (e.g., Bujak and Brinkhuis, 1998; Crouch et al., 2001; Crouch, 2001). The FO of representatives of the genus heralds this phase during the latter half of the Paleocene. Many zonation schemes, like that of Wilson (1988) from New Zealand, make use of this aspect for recognition of the late Paleocene. In relevant samples from Hole 1172D, representatives of Apectodinium are sparse at best and an acme is conspicuously absent. This suggests that the typical PETM succession has not been recovered at Site 1172, either due to a hiatus or to core recovery problems (bad luck). Alternatively, because Apectodinium represents a tropical genus, climatic conditions, despite the general warmth at the end of the Paleocene, may just not have allowed a significant manifestation at these paleolatitudes. The Paleocene/Eocene hiatus or core gap may be small, as discussed elsewhere (Röhl et al., submitted [N3]).
The lower Eocene in essence forms a continuation of the upper Paleocene succession, with a relative abundance of species of Deflandrea, Palaeocystodinium, Operculodinium, Hystrichosphaeridium, and Spiniferites, besides typical early Eocene taxa like Dracodinium waipawaense, Samlandia delicata group, and the Pyxidinopsis waipawaensis group being consistently present (cf. Crouch, 2001). Around the early-middle Eocene transition, important FOs include those of the Charlesdowniea edwardsii group, Arachnodinium antarcticum, Membraniphoridium perforatum, and Hystrichokolpoma spinosum. Of significant interregional importance is also the FO of Enneadocysta spp., including Enneadocysta partridgei and Enneadocysta sp. A, near the early/middle Eocene boundary. The succession of these events broadly matches those reported from the New Zealand region (e.g., Wilson, 1988; Hannah and Raine, 1997) from coeval deposits. The calibration against magnetostratigraphy as reached herein now allows more confident dating of early-middle Eocene deposits around Southern Ocean sites (see Table T4). However, some typical Eocene Southern Hemisphere taxa like Arachnodinium antarcticum and Enneadocysta partridgei have an LO at the early/late Oligocene boundary in this area according to Hannah and Raine (1997). Although this aspect is discussed further below (see "Late Eocene-Earliest Oligocene" below) and elsewhere (Sluijs et al., this volume; Stickley et al., submitted [N2]), it may be noted here that these "young" LOs are here considered a result of reworking. Arachnodinium antarcticum, for example, has a consistent top associated with Subchron C18n1n, also at Sites 1170 and 1171 following shipboard studies and updated age models (Stickley et al., this volume; Stickley et al., submitted [N2]; Röhl et al., submitted [N1]).
Although the late Paleocene and early Eocene associations already compose a large portion of typical endemic Antarctic taxa, endemism increases even more toward the end of the early Eocene. The early-middle Eocene transition is marked by a strong influx of endemic (Transantarctic) species like Deflandrea antarctica, Octodinium askiniae, Enneadocysta partridgei, and Vozzhennikovia spp. and/or bipolar (high latitude) taxa like Spinidinium macmurdoense and the Phthanoperidinium echinatum group (cf. Firth, 1996).
The younger part of the Southern Ocean middle Eocene is comparatively less well studied than the underlying part. Only few comparisons may be made to New Zealand (e.g., Wilson, 1988; Strong et al., 1995; Edbrooke et al., 1998; Hannah et al., 1997), Deep-Sea Drilling Project [DSDP] Sites 280 and 281 (Crouch and Hollis, 1996), Seymour Island (Wrenn and Hart, 1988), Scotia Sea (Mao and Mohr, 1995), and southern Argentinian successions (e.g., Guerstein et al., 2002, and references therein), indicating a broad similarity. The younger part of the Southern Ocean middle Eocene appears to be characterized by several important LOs, including those of Membranophoridium perforatum, Hystrichosphaeridium truswelliae, Arachnodinium antarcticum, Hystrichokolpoma spinosum, and Hystricholkopoma truncatum (cf. Wilson, 1988) (see Table T4).
Early late Eocene dinocyst distribution forms a continuation of the middle Eocene pattern. Transantarctic species predominate, and final acmes of Enneadocysta partidgei, the Deflandrea antarctica group, and Spinidinium macmurdoense are recorded. Important FOs in this phase include those of Schematophora speciosa, Aireiana verrucosa, Hemiplacophora semilunifera, and Stoveracysta ornata. Toward the middle late Eocene, FOs of Achomosphaera alcicornu, Reticulatosphaera actinocoronata, and Alterbidinium distinctum and the LO of Schematophora speciosa appear important for interregional correlation. Vozzhennikovia spp. continues to be a common constituent of the associations. The LO of Schematophora speciosa is very close to the LO of abundant Deflandrea antarctica group, and the latter horizon marks a significant change in the associations, including a brief barren interval. Here, on one hand cosmopolitan taxa like Turbiosphaera filosa, Cleistosphaeridium spp., and Lingulodinium machaerophorum become prominent, whereas on the other hand, new species like Deflandrea sp. A and Brigantedinium? sp. dominate the succession. In addition, the FO of Stoveracysta kakanuiensis is recorded. Slightly upsection, in a succession dated by other means as approximately the E/O boundary (sensu GSSP), sediments become barren of organic microfossils to only briefly reappear in the early Oligocene (assigned to Chron C10) (Table T4). In this single productive sample thus far from the Oligocene, virtually all transantarctic Paleogene dinocysts have disappeared (only a single, poorly preserved, probably reworked specimen of Enneadocysta partridgei is recovered). The association in this sample (189-1172A-39X-2, 3-5 cm; 356.13 mbsf) is characterized by the abundance of taxa more typical for Tethyan waters, including an occurrence of Hystrichokolpoma sp. cf. Homotryblium oceanicum (e.g., Brinkhuis and Biffi, 1993; Wilpshaar et al., 1996; Brinkhuis et al., this volume [Site 1168]).
Some of the late Eocene dinocyst events have previously been reported from the Browns Creek section (Cookson and Eisenack, 1965; Stover, 1975). For example, the ranges of Schematophora speciosa, Aireiana verrucosa, Hemiplacophora semilunifera, and Stoveracysta ornata appear useful for regional and even global correlation. Many of the Browns Creek late Eocene dinocysts have been recorded from locations around the world, also in otherwise well-calibrated sections in central and northern Italy, including the Priabonian Type (Brinkhuis and Biffi, 1993; Brinkhuis, 1994). It appears that these index species have slightly earlier tops in this region than they have in Italy (Tethyan Ocean), if the records of Cookson and Eisenack (1965) and Stover (1975) are combined with more recent nannoplankton and magnetostratigraphic studies from the same section (Shafik and Idnurm, 1997). This aspect may be related to the progressive global cooling during the latest Eocene.
The upper Eocene succession at Site 1172 thus comprises the most prominent change in dinocyst associations of the Paleogene, pointing to important environmental changes influencing the site at this time. A similar transition is, albeit in less detail, reported by shipboard palynological analysis from Sites 1170 and 1171. More details on the E-O transition, also from other Leg 189 sites, and paleogeographic and oceanographic implications are presented and discussed presented in Sluijs et al. (this volume), in Stickley et al. (submitted [N2]), and in Huber et al. (submitted [N5]).
The Quaternary record throughout has reasonable palynological recovery (Table T3), whereas the underlying Oligocene-Pliocene interval is apparently barren, an aspect that may be related to changing oceanographic and depositional setting. Possibly, the stronger influence of the relatively warm (oxygen depleted) East Australian Current waters or productivity changes and/or less active bottom currents are involved in this aspect. The associations are typically dominated by oceanic dinocysts like Nematosphaeropsis and Impagidinium spp. (notably Impagidinium aculeatum, Impagidinium paradoxum, and Impagidinium patulum). Protoperidinioid species like Brigantedinium spp. are common in some samples. Occasionally, the cold-water species Impagidinium pallidum is present as well. The overall distribution is very similar to that recorded in the Quaternary interval at Site 1168 (Brinkhuis et al., this volume). These results indicate potential for future paleoceanographic studies involving dinocysts.
Clearly, the present results indicate potential for the application of quantitative palynological (dinocyst) analysis for climatic and environmental reconstructions (except for the upper Oligocene to Pliocene interval). Here, we are principally concerned with providing the overall trends. For this purpose, trends in the relative abundance of terrestrial palynomorphs and offshore (oceanic) dinocysts are depicted in Figure F2. Species marked with (o) in Tables T2 and T3 have been used to generate this curve, making use of previous studies focusing on modern dinocyst distribution (e.g., Rochon et al., 1999) and empirical paleoenvironmental evidence from a wide variety of sources (see, e.g., overviews in Brinkhuis and Biffi, 1993; Brinkhuis, 1994; Stover et al., 1996), including the shipboard study on the middle middle Eocene of Site 1170 (Shipboard Scientific Party, 2001b). In that study, it is shown that Enneadocysta maxima correlate with calcareous nannoplankton optima. Enneadocysta is therefore included in the offshore dinocyst category, seen to reflect relatively oligotrophic, offshore settings.
The upper Maastrichtian-lower upper Eocene succession at Site 1172 was interpreted to reflect relatively warm climatic conditions and very shallow water to restricted marine conditions with marked runoff (Shipboard Scientific Party, 2001a, 2001b). The absence of planktonic foraminifers, and even of calcareous nannofossils, in most parts of the Paleocene-middle Eocene confirms the envisaged overall marginal marine nature of the deposits. Older Maastrichtian sediments were deposited in more open-marine conditions based on higher abundances of calcareous microfossils, more offshore dinocyst assemblages, and few pyritized diatoms. The results of the present study further confirm this interpretation (Fig. F2). Similar reconstructions were proposed for the overall similar KTB successions at Seymour Island (Askin, 1988a, 1988b; 1999). Future studies may reveal more detail, for example, concerning sea level change and the nature of the recorded Milankovitch cyclicities (Röhl et al., submitted [N1]).
The upper middle Eocene is marked by a rather gradual change from an inner neritic setting to more offshore conditions. High sporomorph influx and low-diversity/high-dominance dinocyst assemblages with prominent Deflandrea spp., indicating marked freshwater influence and corresponding eutrophic conditions and, possibly, sluggish circulation, characterize the older Eocene deposits. These evolve into more offshore, deeper marine environments with increased ventilation and bottom water current activity, with prominent Enneadocysta spp. (see also Shipboard Scientific Party, 2001c, and Röhl et al., submitted [N1]). The increased numbers of endemic Antarctic dinocyst species in this phase may indicate concomitant cooling and/or isolation of water masses, whereas warmer episodes may also be recognized. The E-O transition (35.5-33.3 Ma) is marked by a series of distinct stepwise environmental changes, seen to reflect cooling and coeval rapid deepening of the basin (Sluijs et al., this volume; Stickley et al., submitted [N2]). Combined evidence indicates increasing bottom water ventilation and the appearance of highly productive offshore surface waters in outer neritic to bathyal depositional settings associated with the deepening of the Tasmanian Gateway (Stickley et al., submitted [N2]). This trend culminated in the early Oligocene (33-30 Ma) when rigorous ventilation and/or oxygen-rich bottom waters precluded sedimentation of organic matter, despite overall high surface water productivity. The condensed pelagic calcareous sequence contains abundant siliceous microfossils and was deposited in an oceanic bathyal environment. Oligocene to present-day pelagic carbonates were deposited in well-ventilated open-ocean conditions.
The curves of Figure F2 both confirm the broad trend of initial shallow-marine, near continental conditions, evolving into an open oceanic environment. Variations in both curves during the Maastrichtian-early Oligocene may be explained by the influence of eustatic sea level changes, as further research will possibly show in more detail (see also Röhl et al., submitted [N1]). A marginal marine, pro-deltaic setting during the Maastrichtian-middle Eocene matches the low-diversity dinocyst assemblages, with cyclic optima of peridinioid species like Alterbidinium, Cerodinium, Deflandrea, Phthanoperidinium, Spinidinium, and Vozzhennikovia spp. and gonyaulacoid taxa such as Enneadocysta, Operculodinium, and Spiniferites spp. The dinocyst assemblages in this part of the core are very similar to those recorded elsewhere from ancient pro-delta deposits (Brinkhuis et al., 1992; Brinkhuis, 1994). The middle and late Eocene are characterized by a slight increase in diversity, with more consistent occurrences of open-marine, neritic to offshore taxa like Enneadocysta spp., Thalassiphora pelagica, Cleistosphaeridium, and Hystrichokolpoma spp., besides increasing numbers of typical oceanic taxa like Nematosphaeropsis and Impagidinium spp. (cf. Fig. F2) (see also Röhl et al., submitted [N1]).
A general eutrophic nature of the surface waters influencing Site 1172 during the Paleogene is suggested from the high abundance of peridinioid, presumably heterotrophic, species (cf. Brinkhuis et al., 1992). This general pattern matches an initial pro-deltaic setting, changing into a more open-oceanic eutrophic (upwelling?) setting (see for further discussion Sluijs et al., this volume, and Stickley et al., submitted [N2]).