Aretz et al_2011.pdf - ORBi - Université de Liège

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Kölner Forum Geol. Paläont., 19 (2011)
M. ARETZ, S. DELCULÉE, J. DENAYER & E. POTY (Eds.)
Abstracts, 11th Symposium on Fossil Cnidaria and Sponges, Liège, August 19-29, 2011
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Origin of the Great Barrier Reef
John S. JELL
University of Queensland; School of Earth Sciences, University of Queensland, St Lucia, Qld 4120,
Australia; j.jell@bigpond.com
The Great Barrier Reef (GBR) is by far the largest reef province of today’s tropical seas and is World
Heritage listed. It consists of more than 3,500 reefs scattered over a quarter of a million square kilometres
off the east coast of Queensland, stretching 2,300 km from Lady Elliot Island in the south to Torres Strait in
the north, and varying from 350 km wide off Rockhampton to 30 km wide off Cooktown. Less than ten
percent of the province is actual coral reef. The reefs are very variable in size, shape and topography, and
appear randomly distributed. Thus any explanation of the origin of the GBR must explain why such a great
reef province is developed on the northeast coast of the Australian continent, what determines the reefs’
morphology, and what controls their distribution. We are part of the way to understanding these and this
contribution gives an historical perspective of our understanding of these to date.
Although probably sighted by early Portuguese, Spanish, Dutch and French navigators before 1770, it
was Captain James Cook’s description and charts of the reef in his journal of his voyage across the southern
oceans that afforded the fascination with the GBR that followed. Cook saw it as a navigational hazard
describing it as: ’a wall of Coral Rock rising all most perpendicular out of the unfathomable Ocean . . . the
large waves of vast Ocean meeting with so sudden a resistance make a most terrible surf breaking
mountains high’. With settlement of Australia in 1788, charting of the coastline became essential and this
included the reefs of the GBR; many of these expeditions carried naturalists. The first geologists to visit the
reef was J.B. JUKES onboard the ‘Fly’ and in his two volume narrative of the voyage published in1847,
provided the first interpretation of the structure of the GBR (Fig. 1).
The assumption was that the GBR was very
thick and old, formed by subsidence and thus
supporting Charles DARWIN’S new theory on reef
development. The only geological observations
over the next 70 years were focused on the coral
reef problem, W. SAVILLE-KENT supporting
DARWIN and A. Agassiz taking the counter-view.
T.W.E. DAVID although deeply involved in the
Fig. 1: Cross-section of GBR from Jukes (1847)
coral reef problem with the drilling of Funifuti
Atoll did not contribute significantly to the
geological understanding of the GBR.
Following the end of WW1, there was a surge in intetrest in the GBR, and H.C. RICHARDS, professor of
geology at the University of Queensland established the Great Barrier Reef Committee with the goal of
encouraging scientific research on the GBR. RICHARD’S aim was to understand the evolution of the reef, and
to that end, planned to drill several holes across its northern, central and southern parts. By 1937, two wells
were completed, one in the north on Michaelmas Cay off Cairns and the other at Heron Island in the south;
results were published by RICHARDS & HILL (1942). In 1957, a petroleum exploration well was drilled on
Wreck Island to the north of Heron Island. The three wells had similar stratigraphies with 100 – 150m of
reefal material overlying a thinner sequence of foraminiferal carbonates and silicastics, and in turn a much
thicker sequence of marine and terresrial shelf sediments. Foraminiferal studies of the cores suggested that
the lowest part of reefal material was Pliocene. The Heron Island core was re-examined by P.G. FLOOD, and
he distinguish six units within the reefal section, separated by disconformities with the
Pliocene/Pleistocene boundary within the oldest unit (FLOOD 1993). If each unit is interpreted as the
erosional remnant of reefal development during successive high stands, Heron Reef is in the order of 500ka
old, the basal reefal unit corresponding to high stand of isotope stage 13.
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