OFR 151.pdf - CRC LEME

Pliocene. The warm phase correlates with the 'mid' Pliocene warm event recorded
elsewhere at middle-high latitudes in the Southern and Northern hemispheres.
8.1.5 Rainfall
• Unlike marine microfossils, terrestrial fossil floras provide direct information on one
of the major factors (rainfall) promoting chemical weathering. Seaways developing
across Australia helped to maintain high humidity in the interior of the continent
during the mid Cretaceous. Orographic effects and groundwater discharge helped
maintain humid-perhumid microclimates within drying environments during the Late
Tertiary.
• Apart from the Berriasian-Barremian, when climates may have been subhumid in
northwestern Australia, humid to perhumid climates extended across the continent
throughout Early Cretaceous time. On present indications, conditions remained wet
to very wet (humid-perhumid) in central southern and southeastern Australia during
the early Late Cretaceous (Turonian to Early Campanian).
• Rainfall appears to have decreased in northwestern Australia from humid-perhumid in
the Late Campanian-Maastrichtian to sub-humid-humid in the Paleocene. A similar
but less marked decrease is recorded in southwestern Australia. Other regions appear
to have become wetter (perhumid).
• The Early Eocene thermal maximum is associated with perhumid conditions across
the continent, including northwestern and central Australia where rainfall may have
been strongly seasonal (possibly monsoonal). Similar conditions persisted into
Middle-Late Eocene, except that rainfall in central Australia became more variable
(less reliable and more seasonal) and rainfall across basins along the southern margin
became more uniformly distributed.
• By Oligo-Miocene time, subhumid conditions prevailed in north-west Western
Australia although conditions at higher elevations within the Pilbara region remained
sufficiently wet during summer months to support temperate rainforest species.
There is weak evidence for a decrease in rainfall in central and south-west Australia.
Rainfall remained in the perhumid range in the south-east mainland and Tasmania but
may have become less reliable or weakly seasonal.
• By the Late Pliocene, essentially modern rainfall regimes were in existence across
Australia. Conditions on the Southeastern Highlands of New South Wales were
effectively wetter during the mid Pliocene than now. The Yallalie site provides
unequivocal evidence for three periods of aridification, at 2.9 Ma, 2.59 Ma and 2.56
Ma, in south-west Western Australia during the same interval (Middle Pliocene warm
period). The vegetation response is similar to that observed during Quaternary
glacial-interglacial cycles and corresponds broadly with the development of
continental ice sheets in the Northern Hemisphere.
114