the vertical facies seen in drill core from the Gulf of Papua.
The present day sediment distribution on the outer continental shelf shows three major facies (Marshall and
Davies, 1978):
North of Latitude 24S-tropical carbonate and clastic sediments dominated by corals and Halimeda.
Latitude 24–28S – subtropical coralline algal coated
grains (rhodoliths), encrusting foramifera, bryozoa.
South of latitude 28S – branching bryozoan/foram/
molluscan facies.
A similar facies sequence occurs vertically in the Borabi
No. 1 drill hole in the Gulf of Papua (Figure 8a). The bottom to top facies variations mirror those on the present
shelf from south to north, and including the change to foreland basin clastics in the Gulf of Papua. The effects of
drift, therefore, are as shown in Figure 9.
Sea-level variations
Operating relatively in conjunction with subsidence, the
effects of sea-level variations on platform development
on the northeast Australian margin are different on the
continental shelf and the marginal plateaux. On the shelf,
high sea levels are carbonate-dominated and low sea
levels are terrigenous-dominated on shelf and slope, and
unconformities are widespread. However, on the oceanic
plateaus where no terrigenous source occurs, high stands
are reef or periplatform dominated and lowstands are
dominated by unconformity development and caliche formation on the platform and carbonate gravity deposition
and peri-platform deposition on the steep slopes.
Collision
If, as a result of plate motion, a passive margin moves into
a compressional tectonic regime, the carbonate platforms
developed on that margin will be profoundly affected.
They will become embroiled in mountain building and
possibly subduction. These effects are seen on the northern
edge of the Australian craton, which collided with an island
arc complex in the Oligocene. The sequential development
of the platform during collision is shown in Figure 10. This
convergent history, leading to foreland basin development
and mountain building, paradoxically, first led to an expansion of the area of carbonate deposition, but was followed
by contraction, demise, and burial of the carbonates by
clastic detritus (Pigram and Davies, 1987; Davies et al.,
1989). This may be the fate of the whole of the GBR if
Australia’s northern motion is not arrested.
Establishment of reefs in northeast Australia
As a consequence of the processes and architecture
described above, coral reefs have been established on
three occasions (1) in the early to late mid-Miocene
(2) in the uppermost Miocene, and (3) in the Pleistocene.
Reefs first established on the Papuan shelf at Borabi
and Pasca. Seismic (Figure 5) and drill hole data
(Figure 8) show early to mid-Miocene reefs at Borabi
established on pre-reefal red algal banks and also on
a basement high at Pasca. On the Queensland Plateau
(Figures 4 and 5b) reefs established in the Middle Miocene,
once again on red algal banks (Brachert et al., 1993).
On the Marion Plateau (Pigram et al., 1992) an extensive
reef system covered over 400 km of the plateau and was
established and reestablished on the plateau and along
its northern edge (Figures 4 and 5). These reef systems
terminated at different times and for different reasons.
30°S
Temperate
Subtropical
Tropical
40°S
Latitude
50°S
60°S
5°
10°
15°
Surface water temperature (°C)
20°
25°
30°
0
1 0
2 0
3 0
Time (Ma)
40
50
60
Northern
great barrier reef
Southern
great barrier reef
Phosphate
‘spike’
Tropical
Temperate
Subtropical
Q Plio
Miocene
Oligocene
S o u th e r n g r e a t b a r r ie r r e e f
Eocene
Paleocene
0
1 0
2 0
3 0
Time (Ma)
40
50
60
20°S
10°S
0°
N o r th e r n g r e a t b a r r ie r re e f/ g u lf o f p ap ua
Q Plio
Miocene
Oligocene
Eocene
Paleocene
b
a
Great Barrier Reef: Origin, Evolution, and Modern
Development, Figure 7 (a) Projected latitudinal movement of
northeast Australia throughout the Cenozoic. The northern
boundary corresponds to Anchor Cay (presently 9
30
0
S) and the
southern boundary to Heron Island (presently 24
S). (b) Surface
water temperature envelope for the northeast Australian region
throughout the Cenozoic, showing periods when temperatures
were suitable for reef growth. The Miocene “phosphate” spike
which inhibited reef growth is also shown (see Riggs, 1984).
516
GREAT BARRIER REEF: ORIGIN, EVOLUTION, AND MODERN DEVELOPMENT
The present day sediment distribution on the outer continental shelf shows three major facies (Marshall and
Davies, 1978):
North of Latitude 24S-tropical carbonate and clastic sediments dominated by corals and Halimeda.
Latitude 24–28S – subtropical coralline algal coated
grains (rhodoliths), encrusting foramifera, bryozoa.
South of latitude 28S – branching bryozoan/foram/
molluscan facies.
A similar facies sequence occurs vertically in the Borabi
No. 1 drill hole in the Gulf of Papua (Figure 8a). The bottom to top facies variations mirror those on the present
shelf from south to north, and including the change to foreland basin clastics in the Gulf of Papua. The effects of
drift, therefore, are as shown in Figure 9.
Sea-level variations
Operating relatively in conjunction with subsidence, the
effects of sea-level variations on platform development
on the northeast Australian margin are different on the
continental shelf and the marginal plateaux. On the shelf,
high sea levels are carbonate-dominated and low sea
levels are terrigenous-dominated on shelf and slope, and
unconformities are widespread. However, on the oceanic
plateaus where no terrigenous source occurs, high stands
are reef or periplatform dominated and lowstands are
dominated by unconformity development and caliche formation on the platform and carbonate gravity deposition
and peri-platform deposition on the steep slopes.
Collision
If, as a result of plate motion, a passive margin moves into
a compressional tectonic regime, the carbonate platforms
developed on that margin will be profoundly affected.
They will become embroiled in mountain building and
possibly subduction. These effects are seen on the northern
edge of the Australian craton, which collided with an island
arc complex in the Oligocene. The sequential development
of the platform during collision is shown in Figure 10. This
convergent history, leading to foreland basin development
and mountain building, paradoxically, first led to an expansion of the area of carbonate deposition, but was followed
by contraction, demise, and burial of the carbonates by
clastic detritus (Pigram and Davies, 1987; Davies et al.,
1989). This may be the fate of the whole of the GBR if
Australia’s northern motion is not arrested.
Establishment of reefs in northeast Australia
As a consequence of the processes and architecture
described above, coral reefs have been established on
three occasions (1) in the early to late mid-Miocene
(2) in the uppermost Miocene, and (3) in the Pleistocene.
Reefs first established on the Papuan shelf at Borabi
and Pasca. Seismic (Figure 5) and drill hole data
(Figure 8) show early to mid-Miocene reefs at Borabi
established on pre-reefal red algal banks and also on
a basement high at Pasca. On the Queensland Plateau
(Figures 4 and 5b) reefs established in the Middle Miocene,
once again on red algal banks (Brachert et al., 1993).
On the Marion Plateau (Pigram et al., 1992) an extensive
reef system covered over 400 km of the plateau and was
established and reestablished on the plateau and along
its northern edge (Figures 4 and 5). These reef systems
terminated at different times and for different reasons.
30°S
Temperate
Subtropical
Tropical
40°S
Latitude
50°S
60°S
5°
10°
15°
Surface water temperature (°C)
20°
25°
30°
0
1 0
2 0
3 0
Time (Ma)
40
50
60
Northern
great barrier reef
Southern
great barrier reef
Phosphate
‘spike’
Tropical
Temperate
Subtropical
Q Plio
Miocene
Oligocene
S o u th e r n g r e a t b a r r ie r r e e f
Eocene
Paleocene
0
1 0
2 0
3 0
Time (Ma)
40
50
60
20°S
10°S
0°
N o r th e r n g r e a t b a r r ie r re e f/ g u lf o f p ap ua
Q Plio
Miocene
Oligocene
Eocene
Paleocene
b
a
Great Barrier Reef: Origin, Evolution, and Modern
Development, Figure 7 (a) Projected latitudinal movement of
northeast Australia throughout the Cenozoic. The northern
boundary corresponds to Anchor Cay (presently 9
30
0
S) and the
southern boundary to Heron Island (presently 24
S). (b) Surface
water temperature envelope for the northeast Australian region
throughout the Cenozoic, showing periods when temperatures
were suitable for reef growth. The Miocene “phosphate” spike
which inhibited reef growth is also shown (see Riggs, 1984).
516
GREAT BARRIER REEF: ORIGIN, EVOLUTION, AND MODERN DEVELOPMENT