FACIES MODELS IN EXPLORATION — THE CARBONATE PLATFORMS OF NORTH-EAST AUSTRALIA

Abstract

The carbonate platforms of north-east Australia encapsulate a record of tectonic, eustatic, climatic and oceanographic dynamism that has controlled their formation. Collectively, the Great Barrier Reef and the Queensland and Marion Plateaus, together with the rift basins that separate them, define a new model for carbonate platform evolution with important exploration consequences. Cretaceous rifting, Paleocene breakup, Cainozoic northward drift with concomitant climatic changes, Neogene subsidence pulses, and sea-level perturbations have combined to produce tropical carbonate platforms overlying temperate, mixed carbonate/siliciclastic facies. The Great Barrier Reef tropical shelf platform thins to the south; reefs first developed in the north in the Early to Middle Miocene along the west- to east-trending distal margin of a foreland basin. The reefs of the Queensland and Marion Plateaus developed in the Middle Miocene and are the precursors of the carbonate platforms of the central and southern Great Barrier Reef. The Miocene Marion Plateau barrier and platform reefs backstepped to become the Plio-Pleistocene Great Barrier Reef. Three energy- and climate-related carbonate facies associations define new prospecting scenarios: the tropical, high energy reef model; the tropical, low energy, Halimeda bioherm model; and the subtropical, low energy, deep water, red algal/ foram/bryozoan bioherm model. These facies occur within four distinct structural/sedimentological associations: the progradative platform margin, the backstepped platform margin, the foreland basin, and the fault block association. The models can be readily applied to the Gulf of Papua/Torres Shelf and the Canning Basin and may produce exciting new insights into carbonate plays in these areas.