OFR 151.pdf - CRC LEME

Subsequent developments include melding of the above schema into a pan-Australian
palynostratigraphy covering the Late Jurassic-Cretaceous Period by Helby et al. (1987) and
the development of a provisional zonation for central Australia (Macphail 1996c, 1997a).
3.1.2 Tertiary
The key Australian schema is the Esso-BHP zonation, developed to date and correlate
sequences in the Gippsland Basin by Stover and Evans (1973) and Stover and Partridge
(1973). This schema and subsequent revisions (Partridge 1976, 1999) have been extrapolated
to other continental margin and epicontinental basins in southern and central Australia,
including the Bass, Eucla, Hale, Murray-Darling and Ti-tree Basins (Stover and Partridge,
1982, Milne, 1988; Macphail and Truswell 1989, 1993; Macphail 1997a, 1997b, 1999). No
formal zonation exists for Late Cretaceous and Tertiary sequences in northeastern or
northwestern Australia, with the predictable result that zones defined for the Gippsland Basin
are in widespread use as de facto Stages names for these regions.
3.2 Independent age control
Pillans (1998) and Duller (2000) have reviewed the geological contexts and time ranges in
which it is appropriate to use the various geochronometric techniques, such as optically
stimulated luminescence (OSL), cosmogenic isotopes ( 10 Be, 36 Cl, 26 Al), oxygen isotopes and
the uranium series isotopes. Calibrated and correlated age methods include fission track
dating, amino-acid racemisation and palaeomagnetism. Grocke (1998) has discussed the use
of carbon isotopes as a 'chemostratigraphic' tool.
Where possible, the age of zone boundaries cited in this study have been independently dated
against the currently accepted International Time Scale using ammonites, planktonic
foraminifera, dinocysts, nannofossils and sequence stratigraphy (Helby et al. 1987, Young
and Laurie 1996, Shafik 1998). Because of provincialism, many of the biostratigraphic tiepoints
with the standard European stages remain uncertain and therefore are subject to
ongoing revision.
An illustration of this is the proposal (H. Brinkhuis pers. comm.) that the first occurrence of
high relative abundances of the marine dinoflagellate genus Apectodinium in the Northern
Hemisphere was part of a globally synchronous event, which can be precisely correlated with
the Paleocene-Eocene Thermal Maximum (PETM). However, in the Gippsland Basin, at
least three species of Apectodinium are recorded in the Paleocene-Eocene transition as defined
by spore-pollen. These are (1) a morphotype of Apectodinium homomorphum characterised
by short processes, which is abundant near the top of the Late Paleocene/Upper
Lygistepollenites balmei Zone, (2) Apectodinium hyperacantha, which reaches its maximum
abundance in the lower part of the early Early Eocene/Lower Malvacipollis diversus Zone,
and (3) a second morphotype of Apectodinium homomorphum characterised by long
processes, which occurs throughout the Early Eocene/M. diversus Zone. If the first 'spike' in
the relative abundance Apectodinium homomorphum species occurred at the Paleocene-
Eocene boundary, then one corollary is that spore-pollen species, whose first occurrence now
defines the Upper Lygistepollenites balmei/Lower Malvacipollis diversus Zone boundary in
the Gippsland Basin, first appeared within the Early Eocene. This in turn implies the
temperature-forced replacement of Austral Conifer Forest by tropical rainforest types took
place over some tens to hundreds of millennia after the PETM.
The Esso-BHP zonation for the Gippsland Basin is under constant review (Partridge 1999)
and absolute ages assigned to the zone boundaries also are subject to on-going revision.
Some radiometric ages used to calibrate Cretaceous palynological zones are considered to be
unreliable (Dettmann et al. 1992). Conversely, the few Potassium-Argon (K/Ar)-dated
microfloras in southeastern Australia fall within the age range proposed for the associated
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