Terrigenous sediment accumulation as a regional control upon the distribution of reef carbonates

Sediment supply to coastal oceans is a primary factor in controlling the occurrence of offshore and nearshore carbonate provinces, particularly coral reefs. Sediment supply to the inner shelf of the central Great Barrier Reef and to the Gulf of Papua is significant, and varies temporally and spatially by several orders of magnitude, as do sediment fluxes of material on the shelf itself. However, coral reefs are common in turbid waters along the inner shelf of the Great Barrier Reef, located where suitable substrates are available. In Halifax Bay, coastal turbid-zone reefs have developed on stable gravel substrates, in water depths of less than 4–5 m. These environments are subject to high rates of coastal sediment transport. Near-bed turbidities of up to 140 nephelometric turbidity units (NTU; equivalent to c. 140 mg 1−1) occur in a wave-dominated coastal boundary layer. In such locations, reef initiation and survival appears to be more strongly controlled by sediment accumulation, and hence substrate availability, than by water quality or sediment flux past the reefs. Sediment accumulation is, in turn, partly controlled by local oceanography and sediment transport.