Controls upon inner‐shelf sedimentation, Cape York Peninsula, in the region of 12°S

Abstract

The far north Queensland coast is characterised by a juxtaposition of coral reefs and terrigenous sediment bodies. Consequently, the distribution and long‐term fate of coastal coral reefs is largely controlled by the processes responsible for sediment dispersal and accumulation. The marine environments which bound the northern Cape York Peninsula receive relatively little modern terrigenous sediment. Estimates of total riverine sediment reaching the coast north of latitude 12°S are 1 Mt y‐1 for the Great Barrier Reef coast and 2.4 Mt y‐2 for the Gulf of Carpentaria coast, corresponding to sediment fluxes (on the shore‐attached wedges) of 2000 g m2y‐1 and 800 g m2y‐1 respectively, and net rates of vertical sediment accumulation of terrigenous material of 0.4 mm y‐1 and 1 mm y‐1. The dispersal of terrigenous sediment appears to be controlled largely by coastline orientation with respect to onshore winds. On the Great Barrier Reef coast, sediment is transported northwards within a well‐defined inner‐shelf zone of terrigenous sediment, and more than half of this sediment is partitioned into the subaerial wedge. No mechanisms are identified for substantial seaward export of sediment seawards off the coastal sediment wedge and into the Great Barrier Reef lagoon. In contrast, on the Gulf of Carpentaria coast, terrigenous sediment is exported seaward and distributed over a shore‐attached wedge tens of kilometres wide. This export 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 Cape York, but appears subordinate to coastal aspect with respect to onshore winds. For the Great Barrier Reef coast in this area, in common with the central Great Barrier Reef, the possibility is reinforced that cyclones are an important control on the timing and volume of terrigenous sediment delivery to the coast, yet play a relatively minor role in the long‐term redistribution and deposition of this material.