OFR 151.pdf - CRC LEME

Figure 11: Early Miocene (20 Ma) palaeogeography (from Veevers et al. 1991)
7.7.1 Palaeogeography
During Oligo-Miocene time, Australia drifted through some 20 0 of latitude (Figures 10-11).
For example, between Early Oligocene and Late Miocene time, northern Tasmania moved
from about palaeolatitude 60 0 S to palaeolatitude 40 0 S whilst Cape York moved from about
palaeolatitude 32 0 to palaeolatitude 11 0 S.
Opening of the Tasmanian Gateway to deepwater circulation at about 33 Ma (Eocene-
Oligocene boundary) initiated continent scale glaciation of Antarctica and profoundly altered
ocean current systems in the Australian region. For example, planktonic foraminifera indicate
that currents that had flowed from Antarctica northward along the western Australian margin
were diverted eastward to become part of the Circumantarctic Current. It is unclear how
currents flowing along the eastern margin of Australia were affected. By this time Tasmania
was separated from the Antarctic continent by 5-8 0 latitude but remained connected to the
mainland via the Flinders Island landbridge. A transient valley glacier formed (Lemonthyme
Glaciation) on the >700 m high Central Plateau of Tasmania during the early part Early
Oligocene (Macphail et al. 1993).
A major fall in global sea levels during the Early Oligocene caused the palaeocoastline to
extend to near the continental shelf edge. Deposits of this age are rare or non-existent except
in the tectonically active south-east where sedimentary sequences accumulated in actively
subsiding basins. Examples are the upper Eastern View Group and Demons Bluff Formations
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