CONTROLS UPON INNER-SHELF SEDIMENTATION, CAPE YORK PENINSULA, IN THE REGION OF 12-DEGREES-S

The far north Queensland coast is characterised by a juxtaposition of coral reefs and terrigenous sediment bodies. Consequently. the distrib ution and long-term fate of coastal coral reefs is largely controlled by the processes responsible for sediment dispersal and accumulation. The marine environment which bound the northern Cape York Peninsula re ceive relatively little modern terrigenous sediment. Estimates of tota l riverine sediment reaching the coast north of latitude 12 degrees S are 1 Mt y(-1) for the Great Barrier Reef coast and 2.4 Mt y(-1) for t he Gulf of Carpentaria coast, corresponding to sediment fluxes (on the shore-attached wedges) of 2000 g m(-2) y(-1) and 800 g m(-2) y(-1) re spectively, and net rates of vertical sediment accumulation of terrige nous material of 0.4 mm y(-1) and 1 mm y(-1). The dispersal of terrige nous sediment appears to be controlled largely by coastline orientatio n with respect to onshore winds. On the Great Barrier Reef coast, sedi ment is transported northwards within a well-defined inner-shelf zone of terrigenous sediment, and more than half of this sediment is partit ioned into the subaerial wedge, No mechanisms are identified for subst antial seaward export of sediment seawards off the coastal sediment we dge and into the Great Barrier Reef lagoon. In contrast, on the Gulf o f Carpentaria coast, terrigenous sediment is exported seaward and dist ributed over a shore-attached wedge tens of kilometres wide. This expo rt is probably caused by near-bed return flows generated by winds with near-normal incidence to the coast. Low sediment supply thus plays a role in determining the sedimentation patterns and rates in the ocean off Cope York, but appears subordinate to coastal aspect with respect to onshore winds. For the Great Barrier Reef coast in this area, in co mmon with the central Great Barrier Reef, the possibility is reinforce d that cyclones are an important control on the timing and volume of t errigenous sediment delivery to the coast, yet play a relatively minor role in the long-term redistribution and deposition of this material.