Geology Reference
In-Depth Information
10°S
130°E
140°E
10°S
120°E
150°E
Gulf of
Carpent-
aria
Barkly
Tablelands
20°S
Continental-Scale Tilting
Fig. 10.46
Dynamic topography
and continental-scale tilting of
the Australian Plate.
A. Asymmetric mid-Miocene
shoreline records provide clear
evidence for differential tilting of
the Australian continent around a
southeast-trending axis. The
shoreline is displaced up to 300 km
inland and 250 m above sea level in
southern Australia, but lies up to
200 km offshore in northern
Australia. Spectacular geomorphic
examples of displaced Neogene
shorelines are from the northern
edge of the Nullarbor Plain,
where numbers delineate the
topographic profiles of Fig. 10.47.
B. Geodynamic forces on the
Indo-Australian Plate margins.
Primarily subduction and/or
collision boundaries on the north
and east “pull” the plate downward.
Spreading ridges on the south and
west “push” the plate upward.
Together, these forces drive a
down-to-the-north tilt of the plate.
Eyre
Basin
1
3
2
30°S
30°S
Murray
Basin
Nullarbor
Plain
4
Eucla Basin
Mid-Miocene Shoreline
Gippsland
Basin
Otway
Basin
Seaward Shoreline Migration
40°S
Landward Shoreline Migration
Topographic Proiles
A
1 2
L
sz: Subduction Zone
ia: Island Arc
cb: Collisional Boundary
Plate Driving Force
Plate Resisting Force
Ridge Push Force
Modeled Stresses
Dynamic
Forces
U P
B
shoreline in southern Australia sits as much as
300 km inland, whereas it lies up to 200 km
offshore in northern Australia. These offset
shorelines record
lines and for progressive long-wavelength tilting
(Sandiford, 2007). Remarkably flat shoreline
platforms that are 25-40 km wide, yet contain
only 5-15 m of relief, delineate the Eocene and
mid-Miocene shorelines (Fig. 10.47A). The mid-
Miocene shoreline marking the northern limit of
the Nullarbor Plain trends inland to the north-
northwest for over 700 km and rises from about
50 m to over 250 m above sea level across that
distance (Fig. 10.47B). With respect to the recon-
structed tilt axis, this transect lies farther away
from the axis as it moves inland (Fig. 10.46),
such that the higher mid-Miocene shoreline that
∼
300 m of north-down tilt at a
∼
rate of
20 m/Myr (Sandiford and Quigley, 2009).
The observation that last interglacial shorelines
appear differentially offset across the continent
by about 2 m (Murray-Wallace and Belperio,
1991) suggests that the tilting today is being
sustained at the average Neogene rate.
The broad Nullarbor Plain and Murray Basin
in southern Australia (Fig. 10.46) provide some
of the clearest evidence for abandoned shore-
