Late Eocene Early Oligocene Dinocysts

At the Tasmanian Gateway, the early Late Eocene dinocyst distribution forms a continuation of the Middle Eocene pattern. ''Transantarctic Flora'' species predominate, and final acmes of Enneadocysta partridgei, the Deflandrea antarctica group and Spinidinium macmurdoense are recorded (Fig. 8.10). Important first occurrences (FOs) in this phase include those of Schematophora speciosa, Aireiana verrucosa, Hemiplacophora semilunifera and Stoveracysta ornata. Towards the middle Late Eocene, FOs of Achomosphaera alcicornu, Reticulatosphaera actinocoronata and Alterbidi-nium distinctum and the LO of S. speciosa appear important for interregional correlation, as is the FO of Stoveracysta kakanuiensis. Vozzhennikovia spp. continues to be a common constituent of the associations (Sluijs et al., 2003).

Typically, sediments representing the E/O transition are barren of organic microfossils in all ODP Leg 189 records; dinocysts briefly reappear in the Early Oligocene (assigned to Chron C11-1r; Stickley et al., 2004). In this single productive sample thus far from the Early Oligocene, virtually all Transantarctic Palaeogene dinocysts have disappeared (only a single, poorly preserved, probably reworked specimen of E. partridgei was recovered;

Late Middle Eocene (~ 40 Ma) Bartonian

Early Middle Eocene (~ 45 Ma) Lutetian

Late Middle Eocene (~ 40 Ma) Bartonian

Early Middle Eocene (~ 45 Ma) Lutetian

Early Oligocene 30 Ma) Rupelian

Late Oligocene (~ 25 Ma) Chattian

Miocene (- 20 Ma) Burdigalian

Endemics dominant (> 50 %) # Endemics present (5 - 50 %) 9 No or rare endemics (<5%) O Barren ot dinotlagellate cysts

Early Oligocene 30 Ma) Rupelian

Late Oligocene (~ 25 Ma) Chattian

Miocene (- 20 Ma) Burdigalian

Endemics dominant (> 50 %) # Endemics present (5 - 50 %) 9 No or rare endemics (<5%) O Barren ot dinotlagellate cysts

Figure 8.10: Circum-Antarctic geographical distribution maps (Late Paleocene-Miocene) showing dinocyst endemism. Maps derived from the Ocean Drilling Stratigraphic Network (ODSN). Black areas indicate (continental) blocks that are mostly sub-aerial. Note that several blocks shown in black were partly submerged (e.g., the Ross Sea, the southern Australian margin and parts of Argentina). Shaded areas indicate mostly submerged (continental) blocks (e.g., Brown et al., 2006).

Brinkhuis et al., 2003). The association in this sample 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., 2003).

Some of the Late Eocene dinocyst events have previously been reported from the South Australian margin, e.g. from the Browns Creek section (Cookson and Eisenack, 1965; Stover, 1975). For example, the ranges of S. speciosa, A. verrucosa, H. semilunifera and S. 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 Section (Brinkhuis and Biffi, 1993; Brinkhuis, 1994). It appears that these index species have slightly earlier LOs 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 (Fig. 8.11).

In the rare sediments covering the E/O transition, more specifically the Oi-1 event, from the Weddell Sea and near the Drake Passage (between South America and the Antarctic Peninsula), dinocysts are typically not preserved (Gradstein et al., 2004). However, in the oldest Oligocene sediments bearing dinocysts, the Transantarctic Palaeogene dinocysts (dominant in the latest recovered Eocene sediments) are replaced by cosmopolitan taxa (Gradstein et al., 2004). This suggests that the changes in dinocyst associations in this area were at least broadly similar compared to those in the Tasman Sector. In contrast, it seems that sediments covering the E/O transition are preserved at Prydz Bay (ODP Site 739). Here a gradual change is observed from the typical Transantarctic Palaeogene dinocysts to the taxa typically found in (post-) Oligocene near-Antarctic records (Warnaar, 2006). However, the (cosmopolitan) taxa that are useful for correlation, as mentioned above, are apparently not present in the Prydz Bay records.

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