OFR 151.pdf - CRC LEME

In the Northern Hemisphere, the K/T event has been linked to the natural selection and
diversification of deciduous plants (Wolfe 1987). An estimated 88% of land-dwelling
vertebrates became extinct in eastern Montana (Sheenan and Fastovsky 1992) even though
molecular evidence suggests at least 100 terrestrial vertebrate clades, including birds and
mammals, survived the culling (Gibbons 1997). In the Southern Hemisphere, probable
fragments of the K/T bolide have been recovered from abyssal sediments in the Pacific Ocean
(Hecht 1996, Kyte 1998), and the K/T boundary is clearly defined in ODP Leg 189 cores
drilled on the East Tasman Plateau east of Tasmania (ODP Leg 198 Initial Reports May,
2000): A single iridium anomaly correlated with the K/T boundary has been recorded on
Seymour Island, Antarctica Peninsula (Elliot et al. 1994).
Although clastic deposition appears to have been continuous across the K/T boundary on
Seymour Island, there is no evidence of any mass extinction event in the macrofossil record.
The same is true in Australia where evidence from the Gippsland Basin indicates plant
extinctions were largely confined to taxa producing highly ornamented pollen, e.g. Proteaceae
(Macphail 1994a). Similar changes are recorded in New Zealand (Raine 1994). In both
instances, the preferred explanation is that the microfloral changes were forced by the
extinction or reduction in faunal pollinators, in particular insects. Because the flora was
adapted to prolonged winter darkness, generalist angiosperm clades, and wind-pollinated
gymnosperms were relatively unaffected. Nevertheless, the point remains that, in
palynological terms at least, conifer-dominated plant communities in southeastern Australia
during the Early Danian were distinctly impoverished relative to their Late Cretaceous
predecessors.
7.1.2 Paleocene-Eocene Thermal Maximum [~55 Ma]
The Paleocene is considered to be a period of overall global warming, although drop stones
found in the mid Paleocene Whangai Formation, North Island of New Zealand may indicate
one or more cooling events if the source is confirmed to be glaciers in Antarctica (Leckie et
al. 1995). The more commonly accepted date for glaciers reaching sea level in Antarctica is
the Middle-Late Eocene (Mackensen and Ehrmann 1992). Conversely, the Paleocene-Eocene
transition was marked by a major reorganisation of terrestrial and oceanic ecosystems, linked
to a short-lived pulse of global warming – the Paleocene-Eocene Thermal Maximum event
(PETM).
This major temperature excursion (see Figure A in Preamble) is arguably one of the most
abrupt (~20 ka) warming events in recent geological time (Zachos et al. 1993, Corfield 1994,
Steineck and Thomas 1996, Kroon et al. 1998). Effects included a dramatic turnover in mid
bathyal ostracodes and planktonic and deep-sea benthic foraminifera in the Southern Ocean
(Lu and Keller 1993, Steinbeck and Thomas 1996), the rapid diversification of planktonic
foraminifera in the tropical Pacific (Kelly et al. 1996), a globally synchronous expansion of
the dinoflagellate genus Apectodinium (H. Brinkhuis pers. comm.) and an equally dramatic
increase in the diversity of mammalian fauna in the holoartic region (Clyde and Gingerich
1998). Peterson (1998) estimates that SSTs at high latitudes and temperatures in the deep
ocean increased by 6-8 0 C for a period of 10 5 years at about 55 Ma. Hallam and Wignall
(1999) have concluded that the benthic extinction event is linked to deep-water oxygen
deficiency via the dramatic switch in the source area for deep water, from high southern
latitudes to subtropical Tethyan waters. Aeolian-transported particles in deep-sea sediments
accumulating at palaeolatitude ~48 0 S show a marked reduction in size for about 0.45 Ma
across the Paleocene/Eocene boundary (Hovan and Rea 1992). In this instance, the
phenomenon is explained in terms of a significant reduction of the strength of zonal winds in
the Southern Hemisphere, which in turn reflect decreased latitudinal thermal gradients
resulting from more effective poleward heat transport.
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