Print this pageMiocene Precursors to Great Barrier Reef
Peter J. Davies, Philip A. Symonds, David A. Feary, Christopher Pigram
Huge reefs of Miocene age are present in the Gulf of Papua north of the present-day Great Barrier Reef and to the east on the Marion and Queensland Plateaus.
In the Gulf of Papua, Miocene barrier reefs formed the northern forerunner of the Great Barrier Reef, extending for many hundreds of kilometers along the eastern and northern margin of the Australian craton within a developing foreland basin. Barrier reefs, slope pinnacle reefs, and platform reefs are seen in seismic sections and drill holes. Leeside talus deposits testify to the high energy impinging on the eastern margin of these Miocene reefs.
The Queensland Plateau is a marginal plateau east of the central Great Barrier Reef and separated from it by a rift trough. Miocene reefs occupied an area of about 50,000 km2 and grew on salt-controlled highs on the western margin of the plateau and on a regional basement high extending from the platform interior to its southern margin. Reef growth has continued to the present day, although two major contractions in the area covered by reefs occurred during the Miocene.
The Marion Plateau is present directly east of the Great Barrier Reef and during the Miocene formed a 30,000-km2 platform with barrier reefs along its northern margin and huge platform reefs and lagoons on the platform interior. These reefs grew on a flat peneplaned surface, the whole area forming a large shallow epicontinental sea.
In all three areas, the middle Miocene formed the acme of reef expansion in the region.
The growth of Miocene reefs in northeast Australia has been critically controlled by structure, climate, paleo-oceanography, and plate motion. Foreland basin reefs in the north contrast with oceanic platform and epicontinental platform reefs of the passive margin to the south. Basement faulting has particularly localized the position of barrier and slope pinnacle reefs. Climate and oceanography, controlled by the northward drift of Australia during the Cenozoic, affected the timing of reef initiation and recolonization following Miocene sea level drop. Flooding by fluvial clastics resulted in the death of the reefs in the Gulf of Papua, but farther south, subsidence and sea level changes combined to effect contraction of the Miocene reefs in some areas, termination of growth in other reas, and a westward shift in the locus of growth from the Marion Plateau to the modern Great Barrier Reef.
AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.