the east by the Coral Sea Basin (Figure 1a and b). The plateau has an average depth of 1,500 m, and covers an area
of about 31,000 km
2 at the 2,000 m isobath. Eastern Fields
Reef, the only modern reef on the Eastern Plateau, is about
45 km across at its widest point, and lies at the crest of the
plateau near its northern margin. Submerged and buried
reefs extend northeast from Eastern Fields Reef beneath
the Moresby Trough (Davies et al., 1988). The northern
and southern plateau margins are controlled by normal
faults; the western margin is more complex, and appears
to be a product of thrusting. The Eastern Plateau is
founded on a complex of tilt blocks bounded by
reactivated normal faults, some of which appear to have
undergone both wrench and reverse movement (Davies
et al., 1988). This deformation appears to have resulted
from Late Oligocene and Miocene tectonism caused by
the development of the New Guinea Orogen to the north
(Pigram and Davies, 1987). This late phase of structuring
is not represented on the other northeast Australian marginal plateaux.
Queensland Plateau
The Queensland Plateau is the largest marginal plateau on
the Australian continental margin and is one of the largest
features of its type in the world (Figure 1a and b). It is
bounded on the northeast by the Coral Sea Basin, on the
west by the Queensland Trough, and on the south by the
Townsville Trough. The plateau is roughly triangular in
shape, and extends over an area of about 165,000 km
2
.
Approximately half of the plateau surface lies above the
1,000 m isobath, with living reef systems at or near present
sea level making up 10–15% of the surface. The largest
modern reef complexes are Tregrosse and Lihou Reefs,
lying along the southern margin of the plateau
(Figure 1a). Both these complexes are nearly 100 km long
from east to west, and 50 and 25 km wide, respectively,
from north to south. The other major areas of modern reef
growth are the Coringa, Willis, and Diana complexes,
which are aligned north to south in the center of the plateau, and the large isolated pinnacles of Flinders, Holmes,
Bougainville, and Osprey Reefs, which lie along the western margin of the plateau (Figure 1). In addition, drowned
reefs have been reported from at least 25 different locations (Taylor, 1977; Mutter, 1977; Davies et al., 1988).
Away from reef areas, the plateau surface is generally
smooth and slopes northward. A distinct terrace at approximately 450–500 m depth connects both the Willis and
Diana reef complexes and the Tregrosse-Lihou-Coringa
reef complexes.
Marion Plateau
The 77,000 km
2 area of the Marion Plateau lies directly
east of the central Great Barrier Reef, and is bounded
along its northern margin by the Townsville Trough and
along its eastern margin by the Cato Trough (Figure 1a).
The present plateau surface forms a deep water extension
of the shelf of the central Great Barrier Reef, with water
depths ranging from 100 m along the western border to
500 m along the eastern margin. At present, reef growth
is restricted to Marion Reef, on the northeastern corner,
and Saumarez Reef, at the southeastern corner of the plateau (Figure 1a).
The Marion Plateau is bounded on three sides by rifts:
the Cato Trough to the east, the Townsville Trough to
the north, and in the west by a series of north–southoriented, narrow half-grabens which separate the plateau
from the Australian continent (Figure 1b). The most northern of these half-grabens appear to join the confluence of
the Townsville and Queensland Troughs. In the early Tertiary, therefore, the Marion Plateau formed a separate marginal plateau. The basement beneath the Marion Plateau is
a planated surface dipping gently northeast (Figure 2d and e).
The only disruption to this surface occurs in the northeast corner where a basement high forms the pedestal on
which Marion Reef developed. Basement beneath the plateau margins is steeply down-faulted into the troughs to
the north and east and was completely transgressed during
the Early Miocene, resulting in the development of an
extensive carbonate platform on which four, progressively
more, restricted reef growth phases occurred, the last of
which is seen today on Marion and Saumarez reefs. Over
most of the platform, shallow water carbonates ceased
with late upper Miocene/Pliocene subsidence.
The Swains Reef and Bunker Highs
The Swains Reef high (Figure 1a and b) is a structural high
some 200 km long and 50 km wide to the southwest of the
Marion Plateau and forming the eastern boundary of the
Capricorn Rift basin (Figure 1b). It is probably a late Cretaceous feature when it formed the eastern side of the
Maryborough basin, but became a prominent late Tertiary
feature when rifting jumped from the Maryborough to the
Capricorn basin and sea floor spreading unzipped northwest in the Cato Trough. Marine conditions were
established over the Swains High probably in the late
Oligocene/early Miocene. It is thought that reefs
established in the Pleistocene. The Bunker High occurs
to the southwest of the Capricorn Basin (Figure 1a and b).
It formed an eastern volcanic source for the Cretaceous
Maryborough Basin and following rifting in the Tasman
Sea, the western edge of the Cainozoic Capricorn Basin.
It was transgressed in the Miocene with shallow water
marine calcarenites and foraminiferal limestones
establishing as precursors to reefs in the Pleistocene of this
southern region.
The Great Barrier Reef
The Great Barrier Reef is a modern reef system which
extends along the northeast Australian margin from
24.30 to 9.30
S (15
of latitude), a distance of 2,300 km
from north of Fraser Island in the south to the Torres
Shelf/Gulf of Papua in the north. There are estimated to
be in excess of 3,600 individual reefs within this area.
GREAT BARRIER REEF: ORIGIN, EVOLUTION, AND MODERN DEVELOPMENT
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