Environmental Changes Documented by Marine Microfossils

Early Palaeogene marine microfossil associations from the circum-Antarctic realm are typically characterized by the dominance of largely endemic

Antarctic organic walled dinocysts and siliceous groups like diatoms and radiolarians over calcareous microfossils (e.g. Brinkhuis et al., 2003; Stickley et al., 2004; Warnaar, 2006). The characteristic endemic dinocyst assemblages reported from Middle and Late Eocene deposits around Antarctica are often referred to as the ''Transantarctic Flora'' (cf. Wrenn and Beckmann, 1982). In fact, Late Cretaceous to (early) Palaeogene organic walled dinocysts from the circum-Antarctic realm are comparatively well known, notably from southern South America, from James Ross and Seymour islands, but also from southeastern Australia and New Zealand, from erratics along the Antarctic margin, from the Ross Sea continental shelf (CIROS; CRP) and from several ocean drill sites (see, e.g. Haskell and Wilson, 1975; Wilson, 1985, 1988; Askin, 1988a,b; Wrenn and Hart, 1988; papers in Duane et al., 1992; Pirrie et al., 1992; Mao and Mohr, 1995; Hannah, 1997; Truswell, 1997; Hannah et al., 2000; Levy and Harwood, 2000a,b; Guerstein et al., 2002).

Meaningful chronostratigraphic calibration of (sub-)Antarctic dinocyst events was a classic problem due to the general absence of other age-indicative biotas and/or magnetostratigraphy or other means of dating in sections in which dinocysts are encountered. The first integrated Oligocene to earliest Miocene biomagnetostratigraphy, including dinocysts, was achieved only relatively recently on the basis of successions drilled during the CRP (e.g. Hannah et al., 1998, 2000). Even more recently, the first magnetos-tratigraphically calibrated Late Maastrichtian to earliest Oligocene dinocyst succession was established on the basis of records drilled during ODP Leg 189, offshore Tasmania (e.g. Brinkhuis et al., 2003; Sluijs et al., 2003; Huber et al., 2004; Stickley et al., 2004). Building on these studies, Warnaar (2006) produced higher resolution records for the ODP 189 holes, and (re)analysed critical intervals from other circum-Antarctic sites like 696, 739, 1090 and 1166.

In the following section, the dinocyst record for the Eocene and Oligocene is documented and the implications for our understanding of palaeoceano-graphy at this time are discussed.

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