OFR 151.pdf - CRC LEME

Inferred climate
The data confirm that conditions remained wet to very wet (humid-perhumid) and cool-cold
(microtherm range) throughout the Aptian and early Albian, but hint that seasonal contrasts in
temperature was reduced during the Late Albian. This is consistent with global warming, but
could equally well reflect the extension of maritime climates into high (~70 0 S) palaeolatitudes
along the Australo-Antarctica Rift System.
2.2.6 South-East Australia
Thick sequences of Aptian-Albian sediments occur in the Otway Basin (Eumeralla
Formation) and the Gippsland Basin (Strzelecki Formation). These formations are routinely
intersected by deeper exploration wells. Microfloral lists are available in open file well
completion reports. Such data document plant successions along the palaeo-southwestern
margin but seldom provide objective information on community dominance.
1. Otway Basin
Few quantitative analyses are available but, based on unpublished observations, Dettmann
(1994) has concluded that the gymnosperm and cryptogam communities were less diverse
than equivalent communities making up Austral Conifer Forest in central Australia.
Inferred climate
Floristic impoverishment typically is associated with very wet microtherm climates. If these
constraints, rather than extended periods of winter darkness, were the major factors
influencing plant diversity in the Otway and Gippsland Basins, then climates at the extreme
southern end of the palaeo-western margin are likely to have been perhumid and seasonally
cold (lower microtherm).
The latter inference is in good agreement with Parrish et al. (1991) who conclude that mean
air temperatures in the region were between 5-8 0 C during the Albian. The restricted
development of Gleicheniaceae fern heath in the Otway relative to the Gippsland Basin
(Dettmann 1994) may reflect habitat differences rather than climate.
2.3 Other records
2.3.1 North-West Australia
Hallam (1984, 1985) has proposed that, beginning at the end of the Aptian, northern
Australia, which then lay between latitudes of ~50 0 S and 60 0 S, was subject to intermittent or
locally high precipitation due to the movement of warm water eastwards into the Tethys
Seaway.
2.3.2 Central Australia
1. Eromanga and Surat Basins
Direct evidence for freezing conditions during winter is provided by dropstones and
glendonites preserved in Aptian-Albian strata in both basins. As for the Valanginian-
Barremian interval, these are interpreted as evidence of a large seasonal influx of ice and cold
fresh water from glaciers occupying uplands to the south and west of the Eromanga Basin
(Frakes et al. 1995, Frakes 1999).
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