Coral reef growth on the shelf margin of the Great Barrier Reef with special reference to the Pompey Complex

Abstract

Several modes of coral reef growth are found along the edge of Australia's Great Barrier Reef (GBR), determined by the morphology and slope of the shelf edge, especially between -50 m and -100 m, and the velocity of tidal currents near the surface. The simplest forms are the flood tide deltaic reefs and ribbon reefs of the far north. The shelf margin of the central GBR is characterized by lines of submerged reefs that continue on the ocean (northeastern) side of the Pompey Reefs, which are the largest and most complex in the entire GBR. Combining interpretations of reef evolution from the simpler marginal reefs with data collected from the Pompey Complex, a model of evolution on a stepped continental shelf margin is developed, involving initiation as ribbon reefs, formation of both ebb and flood tide deltas (which have formed the foundation for further reef growth), and incorporation of at least one line of previously submerged reefs on the open ocean side by progradation of the deltaic structures to form large lagoonal reefs. Although the reefs cover a smaller area than the extensive reefs of the continental shelf, which could have grown only at higher Quaternary sea levels, the smaller area of shelf-marginal reefs may contain a longer record of coral growth than that of the better-known shelf reefs.